Read threshold adjustment techniques for memory

ABSTRACT

Methods, systems, and devices for read threshold adjustment techniques for memory are described. A memory device may read a codeword from a memory array of the memory device using a read threshold having a first value. The memory device may increment one or more counters of the memory device based on reading the codeword. The counter may indicate a quantity of bits of the codeword that correspond to a first logic value. The memory device may detect an error, such as an uncorrectable error, in the codeword based on reading the codeword. The memory device may adjust the read threshold from the first value to the second value based on the quantity of bits indicated by the counter. The memory device may read the codeword using the read threshold having the second value.

CROSS REFERENCE

The present Application for Patent is a continuation of U.S. patentapplication Ser. No. 17/240,938 by Eisenhuth et al., entitled “READTHRESHOLD ADJUSTMENT TECHNIQUES FOR MEMORY,” filed Apr. 26, 2021,assigned to the assignee hereof, and expressly incorporated by referenceherein.

FIELD OF TECHNOLOGY

The following relates generally to one or more systems for memory andmore specifically to read threshold adjustment techniques for memory.

BACKGROUND

Memory devices are widely used to store information in variouselectronic devices such as computers, wireless communication devices,cameras, digital displays, and the like. Information is stored byprograming memory cells within a memory device to various states. Forexample, binary memory cells may be programmed to one of two supportedstates, often corresponding to a logic 1 or a logic 0. In some examples,a single memory cell may support more than two possible states, any oneof which may be stored by the memory cell. To access information storedby a memory device, a component may read, or sense, the state of one ormore memory cells within the memory device. To store information, acomponent may write, or program, one or more memory cells within thememory device to corresponding states.

Various types of memory devices exist, including magnetic hard disks,random access memory (RAM), read-only memory (ROM), dynamic RAM (DRAM),synchronous dynamic RAM (SDRAM), ferroelectric RAM (FeRAM), magnetic RAM(MRAM), resistive RAM (RRAM), flash memory, phase change memory (PCM),3-dimensional cross-point memory (3D cross point), not-or (NOR) andnot-and (NAND) memory devices, and others. Memory devices may bevolatile or non-volatile. Volatile memory cells (e.g., DRAM cells) maylose their programmed states over time unless they are periodicallyrefreshed by an external power source. Non-volatile memory cells (e.g.,NAND memory cells) may maintain their programmed states for extendedperiods of time even in the absence of an external power source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system that supports read thresholdadjustment techniques for memory in accordance with examples asdisclosed herein.

FIG. 2 illustrates a plot of example read distributions that supportread threshold adjustment techniques for memory in accordance withexamples as disclosed herein.

FIG. 3 illustrates an example of a system that supports read thresholdadjustment techniques for memory in accordance with examples asdisclosed herein.

FIG. 4 illustrates a plot of example read distributions that supportread threshold adjustment techniques for memory in accordance withexamples as disclosed herein.

FIG. 5 illustrates an example of a system that supports read thresholdadjustment techniques for memory in accordance with examples asdisclosed herein.

FIG. 6 illustrates a plot of example read distributions that supportread threshold adjustment techniques for memory in accordance withexamples as disclosed herein.

FIG. 7 illustrates an example of a system that supports read thresholdadjustment techniques for memory in accordance with examples asdisclosed herein.

FIG. 8 shows a block diagram of a memory device that supports readthreshold adjustment techniques for memory in accordance with examplesas disclosed herein.

FIGS. 9-11 show flowcharts illustrating a method or methods that supportread threshold adjustment techniques for memory in accordance withexamples as disclosed herein.

DETAILED DESCRIPTION

A memory device may access a memory cell as part of a read operation.For example, the memory cell may output a signal to a sense componentand the sense component may compare the signal to one or more readthresholds (e.g., reference voltages, reference currents, or anycombination thereof). The memory device may determine a logic value ofthe memory cell (e.g., a stored logic value such as 0 or 1 for a binarymemory cell configured to store one bit; 00, 01, 10, or 11 for anon-binary cell configured to store two bits; etc.) in response tocomparing the signal to the one or more read thresholds. As anillustrative example, the memory device may determine that the memorycell is storing a first logic value (e.g., 0) if the signal is below aread threshold or that the memory cell is storing a second logic value(e.g., 1) if the signal is above the read threshold, although anyquantity of thresholds and logic values may be used. In some examplesthe memory device may read a set of bits from a set of memory cells,where the set of bits may be referred to as a codeword. In some cases,the memory device may detect an uncorrectable error in response toreading one or more codewords from the memory cells. For example, theone or more read thresholds may have shifted over time due toprogram-erase (PE) cycles, read disturbances, cross-temperature effects,and the like. Such shifts may result in a quantity of errors that anerror correction code (ECC) or other error correcting scheme of thememory device is unable to correct.

In accordance with the techniques described herein, the memory devicemay implement read threshold adjustment techniques for memory. Suchtechniques may enable the memory device to accurately shift one or moreread thresholds after reading data in which a relatively high quantityof errors is detected (e.g., prior to reading the data again), which maycorrect at least a subset of errors (e.g., an uncorrectable error may beeliminated or become correctable due to the shifted read thresholds).

For example, a memory device may be configured to store data within amemory array as codewords that are balanced or at least nearly balanced,where a balanced codeword may include equal numbers of 1s and 0s. Forexample, a memory device may apply a scrambler (e.g., pseudo-randomscrambler) before storing data and store the scrambled data as acodeword, where the codeword may be balanced or nearly balanced inresponse to the scrambler. In connection with reading data (e.g.,codewords) from the memory array, the memory device may include one ormore counters configured to track a quantity of logic values in thedata.

In some examples, the memory cells may be examples of single level cells(SLCs) (e.g., the memory cells may each store a single logic value orbit such as a 0 or a 1). In such examples, the memory device may comparea signal from the memory cells to a read threshold to identify a logicvalue stored by a cell. The memory device may read a set of memory cellsas part of reading a codeword. The memory device may increment a counterto track a quantity of a logic values in the codeword (e.g., the countermay be incremented if a 1 is read from a memory cell and thus mayindicate a total quantity of 1s in the codeword). If the memory devicedetects that the codeword includes a relatively high quantity of errors(e.g., a quantity of errors that result in an uncorrectable quantity oferrors), the device may be configured to select a direction or magnitudefor shifting the one or more read thresholds using the one or morecounters. By selecting the direction or magnitude for shifting the readthresholds using the counters, the memory device may reduce a quantityof attempts to read a codeword and reduce wear of the memory device(e.g., extend a life of the device due to predicting a correct directionto shift the read threshold relatively consistently), among otherbenefits.

In some examples, the memory device may shift the read threshold inaccordance with the quantity of one or more logic values in the data.For example, the memory device may shift the read threshold in a firstdirection if the quantity of first logic values in the data (e.g., aquantity of 1s) is larger than a second quantity of second logic valuesin the data (e.g., a quantity of 0s). Alternatively, the memory devicemay shift the read threshold in a second direction if the quantity ofthe first logic values is smaller than the quantity of the second logicvalues. In some cases, the memory device may select a magnitude by whichto shift the read threshold in response to the comparison (e.g., if thecounter indicates a relatively high quantity, the memory device mayshift the read threshold by a relatively large amount).

In some examples, the memory cells may be examples of non-binary memorycells as described herein, each of which may store at least two bits ofinformation (e.g., 00, 01, 10, or 11 for memory cells each configured tostore two bits, 000, 111, 011, etc. for memory cells each configure tostore three bits, and so on). Stated alternatively, the memory cells mayeach include two or more levels for bit storage (e.g., a lower bit levelmay store a first bit which may be referred to as a lower bit, an upperbit level may store a second bit which may be referred to as an upperbit, an extra bit level may store a third bit which may be referred toas an extra bit, and so on for any quantity of levels). In someexamples, a level may be referred to as a page (e.g., an upper level maybe referred to as an upper page).

In some examples, the memory device may use a set of counters associatedwith the levels of the memory cells. In some cases, each level may beassociated with a respective counter of the set of counters. Forexample, a first level (e.g., a lower level) may correspond to a firstcounter. The memory device increment the first counter to track aquantity of a logic values in data stored in the first level (e.g., thefirst counter may be incremented if a 1 is read from a lower level ofthe memory cell). The memory device may increment a second countercorresponding to a second level of the memory cells (e.g., an upperlevel) in response to reading data stored in the second level. Forexample, the second counter may indicate a quantity of memory cellswhose stored logic values (e.g., the logic value of a lower bit and anupper bit) result in a logic gate output having a particular value(e.g., a XOR or XNOR logic gate may output a 1 or a 0 based on multiplebits stored by a given memory cell). Such techniques may be used for anyquantity of levels and counters. For example, if the memory cell storesthree bits using a first, second, and third level respectively, thememory device may increment a third counter corresponding to the thirdlevel (e.g., a XOR or XNOR logic gate may output a 1 or a 0 based on alogic value of the lower bit, upper bit, and extra bit stored in amemory cell). Thus, a memory device may use a combination of thecounters to evaluate multiple thresholds at once. For example, thememory device may use a linear combination of the counts of the set ofcounters to determine a direction, magnitude, or both for adjusting themultiple read thresholds.

Additionally or alternatively, the memory device may use a set ofcounters associated with a set of read thresholds, where each counter ofthe set of counters may correspond to a respective read threshold of theset of read thresholds. Each counter may track a quantity of logicvalues stored by the data for a respective read threshold (e.g., a lowerpage read threshold may correspond to a counter indicating a quantity of1s or 0s read from the lower level of the memory cells, two upper bitread thresholds may correspond to two counters indicating a quantity of1s or 0s read from the upper level of the memory cells, and so on). Thememory device may implement logic to determine counts for eachthreshold. For example, the counter values for the upper bit readthresholds may fail to account for logic values being incorrectly readfrom another distribution as described herein. Thus, the memory devicemay adjust a first count by a second count (e.g., an edge or endthreshold count may be subtracted from another threshold count toaccount for distributions improperly leaking across thresholds). Thememory device may iteratively adjust counts in order to determine acount for each read threshold, and the memory device may adjust the readthresholds using the adjusted counts.

Features of the disclosure are initially described in the context ofsystems, devices, and circuits as described with reference to FIG. 1 .Features of the disclosure are described in the context of readdistributions and systems as described with reference to FIGS. 2-8 .These and other features of the disclosure are further illustrated byand described with reference to an apparatus diagram and flowcharts thatrelate to read threshold adjustment techniques for memory as describedwith reference to FIGS. 9-11 .

FIG. 1 is an example of a system 100 that supports read thresholdadjustment techniques for memory in accordance with examples asdisclosed herein. The system 100 includes a host system 105 coupled witha memory system 110.

A memory system 110 may be or include any device or collection ofdevices, where the device or collection of devices includes at least onememory array. For example, a memory system 110 may be or include aUniversal Flash Storage (UFS) device, an embedded Multi-Media Controller(eMMC) device, a flash device, a universal serial bus (USB) flashdevice, a secure digital (SD) card, a solid-state drive (SSD), a harddisk drive (HDD), a dual in-line memory module (DIMM), a small outlineDIMM (SO-DIMM), or a non-volatile DIMM (NVDIMM), among otherpossibilities.

The system 100 may be included in a computing device such as a desktopcomputer, a laptop computer, a network server, a mobile device, avehicle (e.g., airplane, drone, train, automobile, or other conveyance),an Internet of Things (IoT) enabled device, an embedded computer (e.g.,one included in a vehicle, industrial equipment, or a networkedcommercial device), or any other computing device that includes memoryand a processing device.

The system 100 may include a host system 105, which may be coupled withthe memory system 110. In some examples, this coupling may include aninterface with a host system controller 106, which may be an example ofa control component configured to cause the host system 105 to performvarious operations in accordance with examples as described herein. Thehost system 105 may include one or more devices, and in some cases mayinclude a processor chipset and a software stack executed by theprocessor chipset. For example, the host system 105 may include anapplication configured for communicating with the memory system 110 or adevice therein. The processor chipset may include one or more cores, oneor more caches (e.g., memory local to or included in the host system105), a memory controller (e.g., NVDIMM controller), and a storageprotocol controller (e.g., PCIe controller, serial advanced technologyattachment (SATA) controller). The host system 105 may use the memorysystem 110, for example, to write data to the memory system 110 and readdata from the memory system 110. Although one memory system 110 is shownin FIG. 1 , the host system 105 may be coupled with any quantity ofmemory systems 110.

The host system 105 may be coupled with the memory system 110 via atleast one physical host interface. The host system 105 and the memorysystem 110 may in some cases be configured to communicate via a physicalhost interface using an associated protocol (e.g., to exchange orotherwise communicate control, address, data, and other signals betweenthe memory system 110 and the host system 105). Examples of a physicalhost interface may include, but are not limited to, a SATA interface, aUFS interface, an eMMC interface, a peripheral component interconnectexpress (PCIe) interface, a USB interface, a Fiber Channel interface, aSmall Computer System Interface (SCSI), a Serial Attached SCSI (SAS), aDouble Data Rate (DDR) interface, a DIMM interface (e.g., DIMM socketinterface that supports DDR), an Open NAND Flash Interface (ONFI), and aLow Power Double Data Rate (LPDDR) interface. In some examples, one ormore such interfaces may be included in or otherwise supported between ahost system controller 106 of the host system 105 and a memory systemcontroller 115 of the memory system 110. In some examples, the hostsystem 105 may be coupled with the memory system 110 (e.g., the hostsystem controller 106 may be coupled with the memory system controller115) via a respective physical host interface for each memory device 130included in the memory system 110, or via a respective physical hostinterface for each type of memory device 130 included in the memorysystem 110.

Memory system 110 may include a memory system controller 115 and one ormore memory devices 130. A memory device 130 may include one or morememory arrays of any type of memory cells (e.g., non-volatile memorycells, volatile memory cells, or any combination thereof). Although twomemory devices 130-a and 130-b are shown in the example of FIG. 1 , thememory system 110 may include any quantity of memory devices 130.Further, where memory system 110 includes more than one memory device130, different memory devices 130 within memory system 110 may includethe same or different types of memory cells.

The memory system controller 115 may be coupled with and communicatewith the host system 105 (e.g., via the physical host interface), andmay be an example of a control component configured to cause the memorysystem 110 to perform various operations in accordance with examples asdescribed herein. The memory system controller 115 may also be coupledwith and communicate with memory devices 130 to perform operations suchas reading data, writing data, erasing data, or refreshing data at amemory device 130, and other such operations, which may generically bereferred to as access operations. In some cases, the memory systemcontroller 115 may receive commands from the host system 105 andcommunicate with one or more memory devices 130 to execute such commands(e.g., at memory arrays within the one or more memory devices 130). Forexample, the memory system controller 115 may receive commands oroperations from the host system 105 and may convert the commands oroperations into instructions or appropriate commands to achieve thedesired access of the memory devices 130. And in some cases, the memorysystem controller 115 may exchange data with the host system 105 andwith one or more memory devices 130 (e.g., in response to or otherwisein association with commands from the host system 105). For example, thememory system controller 115 may convert responses (e.g., data packetsor other signals) associated with the memory devices 130 intocorresponding signals for the host system 105.

The memory system controller 115 may be configured for other operationsassociated with the memory devices 130. For example, the memory systemcontroller 115 may execute or manage operations such as wear-levelingoperations, garbage collection operations, error control operations suchas error-detecting operations or error-correcting operations, encryptionoperations, caching operations, media management operations, backgroundrefresh, health monitoring, and address translations between logicaladdresses (e.g., logical block addresses (LBAs)) associated withcommands from the host system 105 and physical addresses (e.g., physicalblock addresses) associated with memory cells within the memory devices130.

The memory system controller 115 may include hardware such as one ormore integrated circuits or discrete components, a buffer memory, or acombination thereof. The hardware may include circuitry with dedicated(e.g., hard-coded) logic to perform the operations ascribed herein tothe memory system controller 115. The memory system controller 115 maybe or include a microcontroller, special purpose logic circuitry (e.g.,a field programmable gate array (FPGA), an application specificintegrated circuit (ASIC), a digital signal processor (DSP)), or anyother suitable processor or processing circuitry.

The memory system controller 115 may also include a local memory 120. Insome cases, the local memory 120 may include read-only memory (ROM) orother memory that may store operating code (e.g., executableinstructions) executable by the memory system controller 115 to performfunctions ascribed herein to the memory system controller 115. In somecases, the local memory 120 may additionally or alternatively includestatic random access memory (SRAM) or other memory that may be used bythe memory system controller 115 for internal storage or calculations,for example, related to the functions ascribed herein to the memorysystem controller 115. Additionally or alternatively, the local memory120 may serve as a cache for the memory system controller 115. Forexample, data may be stored in the local memory 120 if read from orwritten to a memory device 130, and may be available within the localmemory 120 for subsequent retrieval for or manipulation (e.g., updating)by the host system 105 (e.g., with reduced latency relative to a memorydevice 130) in accordance with a cache policy.

Although the example of memory system 110 in FIG. 1 has been illustratedas including the memory system controller 115, in some cases, a memorysystem 110 may not include a memory system controller 115. For example,the memory system 110 may additionally or alternatively rely upon anexternal controller (e.g., implemented by the host system 105) or one ormore local controllers 135, which may be internal to memory devices 130,respectively, to perform the functions ascribed herein to the memorysystem controller 115. In general, one or more functions ascribed hereinto the memory system controller 115 may in some cases instead beperformed by the host system 105, a local controller 135, or anycombination thereof. In some cases, a memory device 130 that is managedat least in part by a memory system controller 115 may be referred to asa managed memory device. An example of a managed memory device is amanaged NAND (MNAND) device.

A memory device 130 may include one or more arrays of non-volatilememory cells. For example, a memory device 130 may include NAND (e.g.,NAND flash) memory, ROM, phase change memory (PCM), self-selectingmemory, other chalcogenide-based memories, ferroelectric RAM (FeRAM),magneto RAM (MRAM), NOR (e.g., NOR flash) memory, Spin Transfer Torque(STT)-MRAM, conductive bridging RAM (CBRAM), resistive random accessmemory (RRAM), oxide based RRAM (OxRAM), and electrically erasableprogrammable ROM (EEPROM). Additionally or alternatively, a memorydevice 130 may include one or more arrays of volatile memory cells. Forexample, a memory device 130 may include random access memory (RAM)memory cells, such as dynamic RAM (DRAM) memory cells, synchronous DRAM(SDRAM) memory cells, or SRAM memory cells.

In some examples, a memory device 130 may include (e.g., on a same dieor within a same package) a local controller 135, respectively, whichmay execute operations on one or more memory cells of the memory device130. A local controller 135 may operate in conjunction with a memorysystem controller 115 or may perform one or more functions ascribedherein to the memory system controller 115.

In some cases, a memory device 130 may be or include a NAND device(e.g., NAND flash device). A memory device 130 may be or include amemory die 160. For example, in some cases, a memory device 130 may be apackage that includes one or more dies 160. A die 160 may, in someexamples, be a piece of electronics-grade semiconductor cut from a wafer(e.g., a silicon die cut from a silicon wafer). Each die 160 may includeone or more planes 165, and each plane 165 may include a respective setof blocks 170, where each block 170 may include a respective set ofpages 175, and each page 175 may include a set of memory cells.

In some cases, a NAND memory device 130 may include memory cellsconfigured to each store one bit of information, which may be referredto as SLCs. Additionally or alternatively, a NAND memory device 130 mayinclude memory cells configured to each store multiple bits ofinformation, which may be referred to as MLCs if configured to eachstore two bits of information, as tri-level cells (TLCs) if configuredto each store three bits of information, as quad-level cells (QLCs) ifconfigured to each store four bits of information, or more genericallyas multiple-level or multi-bit memory cells. Multiple-level memory cellsmay provide greater density of storage relative to SLC memory cells butmay, in some cases, involve narrower read or write margins or greatercomplexities for supporting circuitry.

In some cases, planes 165 may refer to groups of blocks 170, and in somecases, concurrent operations may take place within different planes 165.For example, concurrent operations may be performed on memory cellswithin different blocks 170 so long as the different blocks 170 are indifferent planes 165. In some cases, performing concurrent operations indifferent planes 165 may be subject to one or more restrictions, such asidentical operations being performed on memory cells within differentpages 175 that have the same page address within their respective planes165 (e.g., related to command decoding, page address decoding circuitry,or other circuitry being shared across planes 165).

In some cases, a block 170 may include memory cells organized into rows(pages 175) and columns (e.g., strings, not shown). For example, memorycells in a same page 175 may share (e.g., be coupled with) a common wordline, and memory cells in a same string may share (e.g., be coupledwith) a common digit line (which may alternatively be referred to as abit line).

For some NAND architectures, memory cells may be read and programmed(e.g., written) at a first level of granularity (e.g., at the page levelof granularity) but may be erased at a second level of granularity(e.g., at the block level of granularity). That is, a page 175 may bethe smallest unit of memory (e.g., set of memory cells) that may beindependently programmed or read (e.g., programed or read concurrentlyas part of a single program or read operation), and a block 170 may bethe smallest unit of memory (e.g., set of memory cells) that may beindependently erased (e.g., erased concurrently as part of a singleerase operation). Further, in some cases, NAND memory cells may beerased before they can be re-written with new data. Thus, for example, aused page 175 may in some cases not be updated until the entire block170 that includes the page 175 has been erased.

The system 100 may include any quantity of non-transitory computerreadable media that support read threshold adjustment techniques formemory. For example, the host system 105, the memory system controller115, or a memory device 130 may include or otherwise may access one ormore non-transitory computer readable media storing instructions (e.g.,firmware) for performing the functions ascribed herein to the hostsystem 105, memory system controller 115, or memory device 130. Forexample, such instructions, if executed by the host system 105 (e.g., bythe host system controller 106), by the memory system controller 115, orby a memory device 130 (e.g., by a local controller 135), may cause thehost system 105, memory system controller 115, or memory device 130 toperform one or more associated functions as described herein.

The system 100 may implement read threshold adjustment techniques asdescribed herein. For example, the memory system 110 (or the host system105) may adjust one or more read thresholds using one or more countersas described herein, which may enable the memory system 110 to correctone or more errors (e.g., otherwise uncorrectable errors), reduce aquantity of reading operations for a codeword, extend a life of thememory system 110, or any combination thereof, among other benefits. Forexample, the memory system 110 may include one or more countersconfigured to track a quantity of logic values in data. The memorysystem 110 may be configured to select a direction or magnitude forshifting the one or more read thresholds using the one or more counters.In some examples, the memory devices 130 may include SLCs ormultiple-bit cells (e.g., MLCs, TLCs, QLCs, and so on). Though certainexamples may be described herein in the context of NAND memory cells, itis to be understood that the techniques described herein may be appliedin the context of any type of memory cells.

FIG. 2 illustrates a plot 200 of example read distributions that supportread threshold adjustment techniques for memory in accordance withexamples as disclosed herein. The plot 200 may illustrate examples ofoperations implemented by a system 100 as described with reference toFIG. 1 or another system as described herein. The plot 200 may include avoltage axis 205 and a quantity axis 210 for illustrative clarity,although other metrics may be used (e.g., a current axis or a chargeaxis rather than a voltage axis). Generally, the plot 200 may illustrateexample distributions 215 for the voltages of signals read from (e.g.,in response to reading) memory cells in a memory array and an exampleadjustment 225 of a threshold 220 using one or more counters.

The plot 200 may include a read threshold 220, which may be an exampleof a voltage threshold, though a current threshold or charge thresholdmay additionally or alternative be used. The read threshold 220 may beused as part of one or more access operations (e.g., read operations).For example, a memory device may receive a command to read data from anaddress of a memory array. The data may be a codeword indicated by anaddress in the command. The memory device may access memory cellsassociated with the codeword (e.g., each memory cell included in theaddress) and compare an output of a memory cell to the read threshold220. For example, if a sense component of the memory device detects avoltage lower than the read threshold 220, the memory device may readthe corresponding memory cell as storing a first logic value (e.g., a 0or a 1). Alternatively, if the sense component detects a voltage higherthan the read threshold 220, the memory device may read thecorresponding memory cell as storing a second logic value (e.g., a 1 ora 0).

The plot 200 may include distribution 215-a and distribution 215-b. Thedistributions 215 may illustrate the voltages of signals sensed for aquantity of memory cells from which a codeword is read that are storinga respective logic value. For example, a point on the distribution 215-amay represent a quantity of memory cells storing a respective voltagevalue. The memory cells with voltages on the distribution 215-a may beexamples of memory cells previously written with a first logic value(e.g., 1) and the distribution 215-b may be examples of memory cellspreviously written with a second logic value (e.g., 0). Although shownas parabolic curves for illustrative clarity, it is to be understoodthat the distributions 215 may be any shape or associated with any logicvalue.

The memory device may implement one or more ECC schemes to detect orcorrect errors in the data. For example, the memory device may useerror-correcting cyclic codes such as Bose, Chaudhuri, and Hocquenghen(BCH) codes. Additionally or alternatively, the memory device may uselinear error-correcting codes, such as low-density parity-check (LDPC)codes. It is to be understood that any type of code-based technique orother technique for error correction or detection may be implemented bythe memory device. User data may be stored in the memory array as one ormore codewords. For example, ECC bits may be generated using the ECCscheme and the codeword may include the user data bits and ECC bits(e.g., parity bits).

In some examples, the memory system may implement one or more encoders(e.g., as part of one or more memory devices 130 or a memory systemcontroller 115), which in some cases may be referred to as scramblers,to generate balanced codewords in response to user data to be written tothe memory array, such that the memory array may store balanced ornearly balanced codewords representative of the user data. As anillustrative example, the memory system may use a scrambler or otherencoder to generate a sequence of bits from user data where each bit hasan equal probability of being a 1 or a 0. Thus, a memory device maystore user data (e.g., regardless of the original user data sequence ofbits) in the form of codewords in which bits having a relatively similarprobability of being a 0 or a 1, which may improve a reliability andlifespan of the memory device and reduce read disturbance.

In some examples, the read threshold 220 may deviate from a desiredvalue, which may result in one or more errors in the data. Viewedalternatively, the distributions 215 may shift over time such that anideal location of the read threshold 220 at some later time may bedifferent from an ideal location of the read threshold 220 at some priortime. For example, the ideal location of read threshold 220 may beshifted over time due to PE cycles, read disturbances, cross temperatureeffects, or a combination thereof (e.g., the distributions 215 may shiftover time due to PE cycles, read disturbances, cross temperatureeffects, or a combination thereof). Such shifts may result in a portionof the memory cells being read as incorrect values. For example, memorycells of the distribution 215-b (e.g., written to a second logic valuesuch as a 1 or a 0) that are located to the left of the read threshold220 may be incorrectly read as memory cells of the distribution 215-a.As an illustrative example, memory cells written as a second logic value(e.g., 0) may be read as the first logic value (e.g., 1) due to thevoltage of those memory cells being less than the read threshold 220. Insome examples, such a shift in the read threshold 220 may introduce arelatively large quantity of errors in a codeword, which may result inan detectable but uncorrectable error (e.g., more erroneous bits than anECC scheme of the memory device may correct, but not so many erroneousbits that the ECC scheme of the memory device fails to detect the error,such as a two-bit error if the ECC scheme is a single-error-correctingdouble-error-detecting (SECDED) scheme, for example).

Accordingly, the memory system may adjust the read threshold 220 usingone or more counters. For example, the memory system may use apseudo-random or random scrambler to encode user data to a codeword(e.g., the memory system may include the scrambler, for example, in acontroller of the memory system or elsewhere in the memory system). Insuch an example, the probability that a bit of the codeword is a firstlogic value may be 0.5, although any probabilities or scramblers may beused. The decoder of the memory system may include a counter configuredto count the quantity of bits having a particular logic value within acodeword read from the memory. For example, a counter may increment eachtime a 1 is read as part of the codeword, and the counter value mayindicate the quantity of 1s in the codeword. Alternatively, the countermay track the quantity of bits that are of a second logic value (e.g., aquantity of 0s in the codeword).

For a given codeword, the memory system may compare the quantity (e.g.,count) of bits having a first logic value indicated by the counter to athreshold or a quantity of bits having a second logic value. Forexample, the memory system may compare the quantity to a differencebetween the total quantity of bits in the codeword and the quantity(e.g., if a codeword has 9312 bits, the memory system may compare thequantity to 9312 minus the quantity, as one example). It is to beunderstood that these and any other specific numbers provided herein areexamples provided solely for the sake of illustrative clarity and arenot limiting of the claims. Additionally or alternatively, the memorysystem may compare the quantity to one or more threshold quantities(e.g., the memory system may determine whether the quantity of bitshaving a first logic value is greater than or less than half the bits inthe codeword, or greater than or less than half the bits in the codewordby at least some amount).

The memory system may perform an adjustment 225 in response to thecomparison. For example, the memory system may select a direction, amagnitude, or both to adjust (e.g., shift) the read threshold 220 inresponse to the quantity indicated by the counter. As an illustrativeexample, the memory system may determine that the quantity of 1s in thecodeword is greater than the quantity of 0s or satisfies a thresholdquantity of 1s. The memory system may shift the read threshold 220 in adirection associated with the determination. For instance, the memorysystem may shift the read threshold 220 to the left (e.g., adjust areference voltage for read operations to be relatively smaller) suchthat the read threshold 220 is located relatively closer to thedistribution 215-a. Additionally or alternatively, the memory system maydetermine a magnitude of the adjustment 225 in response to the counter(e.g., a table may indicate the magnitude, the magnitude may scale withthe quantity such that a relatively large quantity of 1s in the codewordcorresponds to a relatively large adjustment 225, etc.). Althoughdescribed as adjusting to the left (e.g., towards distribution 215-a)and tracking the quantity of the first logic value in the codeword forillustrative clarity, any additional or alternative variations may beimplemented by the memory system (e.g., the memory system may adjust tothe right in response to a counter, the memory system may track thequantity of second logic values, and the like). In some examples, thememory system may perform the techniques described herein regardless ofwhether an error is uncorrectable or not (e.g., a relatively highquantity of errors may satisfy a threshold and the memory system mayproactively shift the thresholds using the techniques described hereinto reduce the quantity of errors).

The memory system may perform another read operation after adjusting theread threshold 220. For example, the memory system may read the codewordfrom the memory cells using the adjusted read threshold 220. Byadjusting the read threshold 220 in the selected direction or magnitude,the second read operation may result in a relatively higher or lowerquantity of the first logic value. For example, a lower quantity of 1smay be read due to the read threshold being shifted such that memorycells of the distribution 215-b that were incorrectly read as is in thefirst read operation due to the initial location of the read threshold220 now being correctly read as 0s due to the shifted location of theread threshold 220. Accordingly, a quantity of errors may be reducedsuch that errors may be eliminated or an ECC code may correct anyremaining errors. In some examples, the memory system may performadditional or alternative adjustments 225. For example, if the secondread operation results in another uncorrectable error, the memory systemmay repeat the comparison and adjustment process until a successful readoccurs. Alternatively, the memory system may perform an adjustment in anopposite direction in response to the second uncorrectable error (e.g.,the memory system may shift the threshold to the left for a secondoperation and shift the threshold to the right of the initial readthreshold 220 for a third operation in response to the second operationincluding an uncorrectable error).

As one illustrative example, the memory system may detect an error usingBCH code (e.g., an ECC decoder may be an example of a BCH decoder). Theuser data size may be 1 Kilobyte (KB) (e.g., 8000 bits) and a size ofthe codeword may be 9312 bits, which may support correction of up to 80errors in the data. In other words, for an uncorrectable error to occur,81 or more bits of the data may be flipped to an incorrect value. Thememory system may determine that a first quantity of the bitscorresponding to a first logic value is greater than a second quantityof the bits corresponding to a second logic value (e.g., the codewordwas read with more 1s than 0s or more 0s than 1s). In such cases, theremay be a relatively high probability that the correct direction toadjust the read threshold 220 is the direction that results in arelatively higher quantity of bits corresponding to the second logicvalue (e.g., shifting the threshold left to result in more 0s from thedistribution 215-b). In other words, the memory system may shift thethreshold in a direction that results in a high quantity of bitscorresponding to the second logic value due to determining that thefirst quantity of bits if higher than the second quantity of bits. Forexample, in order for the codeword to be uncorrectable and the directionindicated by the counter to be incorrect, there may be at least

$T + 2 + \left( \frac{9312}{2} \right)$bits that correspond to the first logic value in the data (e.g., in acodeword), where T represents the quantity of bits the ECC code cancorrect. The probability that the original scrambled codeword includedsuch a quantity of bits having the first logic value may be relativelylow, and the probability that the threshold 220 shifting to reduce thequantity of 1s (e.g., to the left) is the correct direction mayaccordingly be relatively high.

As another illustrative example, the memory system may detect an errorusing LDPC code (e.g., an ECC decoder may be an example of a LDPCdecoder). In such examples, the code may correspond to a set quantity oferrors that render codeword uncorrectable. In such examples, theprobability that a direction is a correct direction may be calculated asa product of the probability that the original scrambled codewordincludes the indicated quantity of bits with a first logic value and theprobability that the quantity of bits may result in an uncorrectableerror.

In some examples, the memory system may calculate such probabilitiesdescribed herein and shift the threshold 220 in response to thecalculation. For example, the memory system may use a binomial formulaor other calculation techniques to determine a probability that adirection is correct, and select the direction in response to theprobability. Additionally or alternatively, the memory system may bepre-configured with thresholds and may adjust the threshold 220 inresponse to the pre-configured thresholds. For example, the memorysystem may be configured to shift a direction to reduce the greaterquantity of bits (e.g., if quantity of 1s are greater than quantity of0s in the codeword, shift to a lower voltage threshold 220 such that thequantity of 1s are reduced). Additionally or alternatively, the memorysystem may be configured to store and consult a look-up table and mayadjust the threshold 220 in a direction, magnitude, or both indicated inthe table by a field corresponding to a respective counter value orrange of counter values. The different counter values associated withthe different entries of the look-up table may be in response to suchprobabilities as determined prior to configuration of the memory systemor in response to experimental techniques, for example.

FIG. 3 illustrates an example of a system 300 that supports readthreshold adjustment techniques for memory in accordance with examplesas disclosed herein. In some examples, the system 300 may be an exampleof or include aspects of the system 100 and/or the plot 200 as describedwith reference to FIGS. 1 and 2 . For example, the system 300 mayinclude memory 305, which may be example of a memory array as describedherein (e.g., NAND SLC memory cells). The system 300 may illustrate anexample implementation of adjusting a read threshold using a decoder310, a counter 315, and a comparison component 320. Although shown asseparate for illustrative clarity, the various components of the system300 may be combined or located different than shown (e.g., the decoder310 may include the counter 315 and the comparison component 320 inlogic).

In some examples, the system 300 may include an encoder 335. The encoder335 may be configured to scramble user data into a codeword as describedherein with reference to FIG. 2 . For example, the encoder 335 mayreceive user data and generate a balanced sequence of 0's and 1's usinga scrambler as described herein. The encoder 335 may additionally oralternatively be configured to encode the codeword using an ECC code, tosupport an error detection or correction procedure if later reading thecodeword from the memory 305.

The system 300 may show a data path for performing an adjustment 325 ofa read threshold using the techniques described herein with reference toFIG. 2 . For example, data (e.g., a codeword) may be read from thememory 305. The data may be input to the decoder 310 and the counter315. The decoder 310 may detect an uncorrectable error 330 in responseto decoding the data. In some examples, the decoder 310 may include adescrambler in addition or in the alternative to the ECC decoder. Forexample, the decoder 310 may be configured to descramble the codeword tothe original user data as part of the read operation. Additionally oralternatively, the counter 315 may track a quantity of bits in the datathat correspond to a first logic value (e.g., the counter may incrementeach time a 1 or a 0 is read from a memory cell) as described withreference to FIG. 2 .

The comparison component 320 may receive a quantity of bitscorresponding to the first logic value from the counter 315, anindication that the data includes an uncorrectable error from thedecoder 310, or both. For example, if the decoder 310 detects that theerrors 330 in the data are uncorrectable (e.g., the data includes anuncorrectable quantity of errors for an ECC scheme), the decoder 310 mayindicate the error 330 to the comparison component 320. The comparisoncomponent 320 may compare the quantity of bits to a second quantity ofbits (e.g., a quantity of 0s to a quantity of 1s). In some examples, thecomparison component 320 may compare the quantity of bits indicated bythe counter 315 to one or more thresholds (e.g., determine whether thequantity of bits satisfies, exceeds, or falls below a threshold such ashalf the bits of the codeword, or some number of other thresholds inorder to identify an extent to which the codeword is unbalanced asread).

The memory system may perform an adjustment 325 using a result from thecomparison component 320. For example, if the comparison component 320indicates that the quantity of bits with the first logic value isgreater than the quantity of bits with the second logic value orsatisfies a threshold, the memory system may select a direction toreduce the quantity of bits with the first logic value for a subsequentread operation. As an illustrative example, the memory system maydetermine that the quantity of 1s is greater than the quantity of 0s ina codeword or satisfies a threshold quantity. The memory system may alsodetermine that the error 330 is uncorrectable. For example, a logic gatemay receive the indication that the error 330 is uncorrectable and anindication of whether the quantity of bits with a first logic value isgreater or less than the quantity of bits with a second logic value. Thelogic gate may output a signal indicating that the error 330 isuncorrectable and a first result of the comparison component 320 (e.g.,more is than 0s). In such examples, the memory system may performadjustment 325-a (e.g., the memory system may shift the threshold toobtain a relatively higher quantity of 0s). The direction of the shift,the magnitude of the shift, or both may be in response to the outputs ofthe counter 315 and the comparison component 320. Alternatively, thelogic gate may output a signal indicating that the error 330 isuncorrectable and a second result of the comparison component 320 (e.g.,more 0s than 1s). In such examples, the memory system may performadjustment 325-b (e.g., the memory system may shift the threshold toobtain a relatively higher quantity of 1s). Accordingly, the memorysystem may adjust the read threshold from a first value to a secondvalue, where the direction of the adjustment, the magnitude of theadjustment, or both may be in response to the outputs of the counter 315and the comparison component 320. After adjusting the read threshold,the memory system may read the codeword using the read threshold havingthe second value. Such process may repeat as needed until a codeword isread that is error-free or correctable by the decoder 310, or until athreshold number of attempts (codeword reads) are performed.

FIG. 4 illustrates a plot 400 of example read distributions that supportread threshold adjustment techniques for memory in accordance withexamples as disclosed herein. The plot 400 may be an example ofoperations implemented by a system 100 as described with reference toFIG. 1 . The plot 400 may implement aspects of the plot 200 or thesystem 300 as described with reference to FIGS. 2 and 3 , respectively.Generally, the plot 400 may illustrate example distributions 415 for MLCdata in a memory array. As an illustrative example, the plot 400 showsthresholds 420 and distributions 415 for memory cells storing two bits,although aspects of the teachings herein may be extended to memory cellseach storing any quantity of bits.

The plot 400 may include a read threshold 420-a, a read threshold 420-b,and a read threshold 420-c, which may be examples of voltage thresholds,though current thresholds or charge thresholds may additional oralternatively be used. A memory system may read memory cells using theread thresholds 420. For example, the memory system may compare avoltage of a signal generated in response to reading a memory cell tothe read thresholds 420 and identify a logic value in response tocomparing the voltage.

In some examples, the different thresholds 420 may be associated withrespective bits stored in the memory cell. As an example of a MLC memorycell storing two bits, the threshold 420-b may be associated with arespective first bit of the memory cell, which may be referred to as a“lower bit” or a “lower page bit” of the memory cell. In some cases, thethreshold 420-b may be referred to as a “lower page threshold.” Thethreshold 420-a and the threshold 420-c may be associated with arespective second bit of the memory cell, which may be referred to as an“upper bit” or an “upper page bit” of the memory cell. In some cases,the thresholds 420-a and 420-c may be referred to as “upper pagethresholds.” As an illustrative example, if a voltage signal of a memorycell is less than the threshold 420-b the memory cell may read therespective first bit (e.g., lower page bit) as a 1. The memory systemmay read the respective second bit (e.g., upper page bit) using the readthreshold 420-a if the respective first bit is 1. For example, thememory system may read the second bit as a 1 if the voltage signal isless than the threshold 420-a and a 0 if the voltage signal is greaterthan the threshold 420-a. As another illustrative example, the memorysystem may read the respective first bit as a 0 if the voltage signal isgreater than the read threshold 420-b. The memory system may read therespective second bit as a 0 if the voltage signal is less than the readthreshold 420-c and a 1 if the voltage signal is greater than the readthreshold 420-c.

In such examples, the distribution 415-a may correspond to memory cellswritten with a logic value of 11 (e.g., a lower page bit of 1 and anupper page bit of 1), the distribution 415-b may correspond to memorycells written with a logic value of 01 (e.g., a lower page bit of 1 andan upper page bit of 0), the distribution 415-c may correspond to memorycells written with a logic value of 00 (e.g., a lower page bit of 0 andan upper page bit of 0), and the distribution 415-c may correspond tomemory cells written with a logic value of 10 (e.g., a lower page bit of0 and an upper page bit of 1). In some examples, the logic values,distributions 415, and read thresholds 420 may be different thandescribed (e.g., distributions 415 and read thresholds 420 may beassociated with different logic values, lower page bits, or upper pagebits). Although shown as parabolic curves for illustrative clarity, itis to be understood that the distributions 415 may be any shape orassociated with any logic value.

In some examples, one or more of the distributions 415 may becomeshifted over time such that the one or more read thresholds 420 deviatefrom an ideal read threshold, which may result in one or more errors inthe data. For example, the distributions 415 may become shifted overtime due to PE cycles, read disturbances, cross temperature effects, ora combination thereof. The shift may result in a portion of the memorycells being read as storing incorrect values. For example, memory cellsof the distribution 215-b (e.g., written to a second logic value such asa 01) that are located to the left of the read threshold 420-a may beincorrectly read as memory cells of the distribution 215-a, memory cellsof the distribution 215-c (e.g., written to a third logic value such as00) that are located to the left of the read threshold 420-b may beincorrectly read (e.g., read as 01), and the like. As an illustrativeexample, memory cells written with a second logic value (e.g., 01) maybe read as storing the first logic value (e.g., 11) due to the voltageof those memory cells being less than the read threshold 420-a. In someexamples, such a shift in the read thresholds 420 may introduce arelatively large quantity of errors in a codeword, which may result inan error that is detectable but uncorrectable by an ECC scheme of thememory system.

Accordingly, the memory system may adjust one or more read thresholds420 using one or more counters. For example, the memory system may use apseudo-random or random scrambler to encode user data to generate data,which may be stored in a memory array as a representation of the userdata. In such an example, the probability that a bit of the data maycorrespond to one of four logic values may be 0.25, although anyquantity of bits, logic values, probabilities, or scramblers may beused. The decoder of the memory system may include one or more countersconfigured to increment as the memory system reads the data from thememory.

In some examples, such as for multi-bit cells (e.g., MLC, TLC, QLC,etc.) configured to store two or more bits of information, the memorysystem may implement multiple counters. For example, a memory cell ofthe set of memory cells may include two or more levels for bit storage.In the example of a MLC cell shown in FIG. 4 , a lower bit may be storedon a lower page (e.g., a lower level) of the memory cell and an upperbit may be stored in an upper page (e.g., an upper level) of the memorycell, as described above. As an illustrative example, if the lower bithas a logic value of 1, the voltage of the memory cell may be written tothe left of the lower page read threshold 420-b. In such an example, theupper bit may be a logic value of 1 if written to the left of the upperpage read threshold 420-a or 0 if written to the right. As anotherexample, the lower bit may have a logic value of 0 and written to theright of the lower page read threshold 420-b and an upper bit value of 0may be written to the left of the upper page read threshold 420-c. Insome examples, data may be stored in the memory cells such that acodeword is written and read on a respective level (e.g., each bit of acodeword may be stored on a lower level of the memory cells and each bitof a second codeword may be stored on an upper level of the memorycells).

In some examples, the memory system may use a set of counters associatedwith the levels of the memory cells. For example, each level (e.g.,page) may be associated with a respective counter. In the example ofFIG. 4 with an upper level and a lower level, the memory system mayinclude a first counter associated with the read threshold 420-b and asecond counter associated with the read thresholds 420-a and 420-c. Insuch examples, the memory system may increment the first counter in aSLC manner. For example, the first counter may be incremented to track aquantity of memory cells storing a lower page bit logic value of 0 or 1.

The memory system may increment the second counter using one or morelogic gates. For example, the memory system may include logic circuitry(e.g., one or more Boolean or other logic gates) and may increment acounter in response to an output of the logic circuitry. The memorysystem may adjust the thresholds 420 using the counter indicating aquantity of memory cells having a first result of the logic gate (e.g.,the memory system may compare the quantity to a threshold or a secondquantity of memory cells having a second result and adjust thethresholds 420 associated with the counter using the comparison). Insome cases, the logic circuitry may include an XNOR logic gate. Forexample, the upper page bit and the lower page bit of a same memory cellmay be input to the XNOR logic gate. The XNOR logic gate may beconfigured to output a first logic value (e.g., 1) if two inputs are thesame and output a second logic value (e.g., 0) if the two inputs aredifferent, the two inputs including the respective first bit of a memorycell (e.g., the lower page bit) and the respective second bit of thememory cell (e.g., the upper page bit). Additionally or alternatively,other logic gates may be used for one or more counters (e.g., XOR logicgates). For example, the XOR logic gate may be configured to output afirst logic value (e.g., 1) if the two inputs (e.g., the lower page bitand the upper page bit) are different.

Accordingly, the memory system may implement an algorithm to determine adirection or magnitude of adjustment of the read thresholds 420 for anyquantity of levels (e.g., bits stored by a memory cell) using the valuesindicated by the counters. The algorithm may include determining excesslogic values (e.g., excess 1s) stored across each level and shifting theread thresholds 420 in a magnitude or direction in response to the totalnumber of excess 1s or 0s. For example, the memory system may incrementthe first counter in the SLC manner as described above (e.g., the memorysystem may count the quantity of 1s which may be used to determineexcess is in the lower bit level of the data). The memory system mayincrement the second counter using a logic operation (e.g., XNOR) of thelower bit and the upper bit. Thus, the memory system can determineexcess bits stored to the right of the read thresholds 420-a and 420-c.The memory system may perform such operations for further counters ifmore than two bits are stored in the cell (e.g., for TLC, the memorysystem may XOR all three bits as inputs, track the quantity of 1s, andsubtract half the memory cells in the data or codeword to calculate thenumber of bits to the left of the 4 extra bit level thresholds). Thus,the memory system may obtain a first count associated with the firstcounter indicating excess is of the lower level, a second countassociated with a second counter indicating excess is in the upperlevel, and so on. For example, the memory system may perform a linearcombination of the values indicated by the counters which will indicatethe total number of excess is across each bit level. For example, thefirst count may be the value of the counter, the second count may be thevalue of the second counter multiplied by two, a third count may be thevalue of a third counter multiplied by four, and so on. The resultingvalue (e.g., the linear combination) may be used to determine whichdirection or magnitude to shift all of the thresholds 420. Althoughdescribed as using a linear combination for a total count, it is to beunderstood any technique may be used to evaluate the values indicated bythe counters associated with each level of the memory cells.

Additionally or alternatively, the memory system may use a set ofcounters respectively associated with a set of read thresholds 420. Inother words, each counter of the set of counters may correspond to arespective read threshold 420 of the set of read thresholds 420. Eachcounter may track a quantity of logic values stored by the data for arespective read threshold 420. As an example, a lower page readthreshold 420-b may correspond to a first counter indicating a quantityof 1s read from the lower level of the memory cells, a second countermay correspond to the upper page read threshold 420-a indicating aquantity of is read from a the distribution 415-b, a third counter maycorrespond to the upper page read threshold 420-c indicating a quantityof 1s read from the upper level of the memory cells, and so on formemory cells with more than four read thresholds 420-c. The memorysystem may implement adjustment operations to determine counts for eachthreshold. For example, the memory system may iteratively adjust thecounts for each counter associated with each respective read thresholds420 to determine an accurate count for each read threshold 420. In otherwords, such adjustment operations may account for the counts of othercounters, which may improve an accuracy of the counts. As anillustrative example, the memory system may read an even quantity of 0sand 1s across the read thresholds 420-b due to an amount of 1sincorrectly coming from the distribution 415-d and an equal amount of 0sincorrectly coming from the distribution 415-c. Accordingly, the memorysystem may use the edge read thresholds 420-a and 420-c to firstdetermine a quantity of excess logic values (e.g., bits may only beincorrectly read from one direction, so the excess count is accurate forread thresholds 420 on an edge of the plot 400). The memory system canthen adjust the count of the counter for the read threshold 420-b bysubtracting any excess logic values from the edge thresholds 420, whichresults in an accurate quantity of excess logic values for the readthreshold 420-b. Such techniques may be extended to more read thresholds420 for more bits stored per logic cell.

The memory system may perform an adjustment of one or more readthresholds 420 using the set of counters. For example, the memory systemmay select a direction, a magnitude, or both to adjust (e.g., shift) theread threshold 220 in response to the quantity indicated by the one ormore counters (e.g., the linear combination of the counters to shift thethresholds together, or the memory system may treat each read threshold420 separately and shift in the direction that offsets the quantity ofexcess logic values). As one illustrative example, the linearcombination may indicate that the read thresholds 420 are relatively toofar right and the memory system may adjust the read thresholds 420 tothe left by a magnitude scaled by the quantity of excess logic values(e.g., excess 1s).

The memory system may perform another read operation after adjusting theread thresholds 420. For example, the memory system may read the datausing the adjusted read thresholds 420. By adjusting the read thresholds420 in the selected direction or magnitude in response to the counters,errors in the data may be eliminated or reduced such that an ECC codemay be used to correct any remaining errors or the memory system mayproactively adjust the thresholds to reduce the effects of readdisturbances and the like. In some examples, the memory system mayperform additional or alternative adjustments 225. For example, if thesecond read operation results in another uncorrectable error or arelatively high quantity of errors, the memory system may repeat thecomparison and adjustment process until a successful read occurs.Alternatively, the memory system may perform an adjustment in anopposite direction in response to the second uncorrectable error (e.g.,the memory system may shift the thresholds a first direction for asecond operation and shift the thresholds to an opposite direction froman initial location for a third operation in response to the secondoperation including an uncorrectable error) or if the quantity of errorsincreases after the adjustment.

While shown as two bits per cell for illustrative clarity, it is to beunderstood that the concepts described with reference to FIG. 4 may beimplemented for other cell types storing any quantity of bits (e.g.,other multi-bit cells such as TLC or QLC). For example, a TLC system mayinclude 7 thresholds 420 and use one or more counters to adjust thethresholds 420 as described herein with reference to FIGS. 6 and 7 .

FIG. 5 illustrates an example of a system 500 that supports readthreshold adjustment techniques for memory in accordance with examplesas disclosed herein. In some examples, the system 500 may be an exampleof or include aspects of the system 100, the plot 200, the system 300,and/or the plot 400 as described with reference to FIGS. 1-4 . Forexample, the system 500 may include memory 505, which may be example ofa memory array as described herein (e.g., an array of NAND multi-bitmemory cells). The system 500 may illustrate an example implementationof adjusting a read threshold using a decoder 510, one or more counters515, and a comparison component 520. Although shown as separate forillustrative clarity, the various components of the system 500 may becombined or located different than shown (e.g., the decoder 510 mayinclude the counters 515 and the comparison component 520 in logic).

In some examples, the system 500 may include an encoder 535. The encoder535 may be an example of an encoder as described herein (e.g., anencoder 335). For example, the encoder 535 may be configured to scrambleuser data into a codeword as described herein with reference to FIGS.2-4 . For example, the encoder 535 may receive user data and generate abalanced sequence of 0's and 1's using a scrambler. The encoder 535 mayadditionally or alternatively be configured to encode the codeword usingan ECC code, to support an error detection or correction procedure iflater reading the codeword from the memory 505.

The system 500 may show a data path for performing one or moreadjustments 525 of one or more read thresholds using the techniquesdescribed herein, including with reference to FIG. 2 . For example, data(e.g., a codeword) may be read from the memory 505. The data may beinput to the decoder 510. The data may also be input to the counter515-a, the counter 515-b, or both. The decoder 510 may detect anuncorrectable error 530 in response to decoding the data. Additionallyor alternatively, the error 530 may be a quantity of errors that satisfya threshold (e.g., the memory system may adjust read thresholds if thequantity of errors satisfies a threshold even if the errors arecorrectable). In some examples, the decoder 510 may include adescrambler in addition or in the alternative to the ECC decoder. Forexample, the decoder 510 may be configured to descramble the codeword tothe original user data as part of the read operation. Additionally oralternatively, the counters 515 may track a quantity of bits in the datathat correspond to a first logic value (e.g., the counter 515-a and/orthe counter 515-b may increment each time a 1 or a 0 is read from arespective first bit or a respective second bit of a memory cell) or aquantity of memory cells that correspond to a first result output by aset of logic circuitry (e.g., the counter 515-a and/or the counter 515-bmay increment each time the logic circuitry outputs a first result or asecond result, such as a 1 if the upper page bit and the lower page bitof a memory cells are the same logic value) as described herein,including with reference to FIG. 4 .

In some examples, the system 500 may include logic circuitry 540. Thelogic circuitry 540 may be configured to perform any of the operationsascribed herein to logic circuitry or logic gates in connection withadjusting one or more read thresholds. For example, the logic circuitry540 may include a logic gate (e.g., an XNOR logic gate) configured toreceive one or more inputs (e.g., a respective upper bit and arespective lower bit read from each memory cell associated with acodeword) and output a corresponding result (e.g., a 1 to the counter515-b) indicating whether the two inputs are the same or different,among other possibilities.

The comparison component 520 may receive an indication of a quantity ofbits from the one or more counters 515, an indication that the dataincludes an uncorrectable error 530 from the decoder 510, or anycombination thereof. For example, if the decoder 510 detects that theerrors 530 in the data are uncorrectable (e.g., the data includes anuncorrectable quantity of errors for an ECC scheme), the decoder 510 mayindicate the error 530 to the comparison component 520. The comparisoncomponent 520 may compare the quantity of bits to a second quantity ofbits (e.g., a quantity of 0s to a quantity of 1s) or a threshold asdescribed herein, including with reference to FIG. 4 . Additionally oralternatively, the comparison component 520 or another component maydetermine a linear combination of the first counter 515-a and thecounter 515-b and use the result to determine the direction or magnitudeof an adjustment 525.

The memory system may perform an adjustment 525 in response to a resultfrom the comparison component 520. For example, if the comparisoncomponent 520 indicates that the read thresholds are relatively too farfrom an ideal read threshold location as described herein, the memorysystem may select a direction of adjustment, a magnitude of adjustment,or both in accordance with the magnitude and direction of the count(e.g., to reduce the quantity of bits being incorrectly read as part ofanother distribution due to a current location of the read thresholds,among other examples as described herein with reference to FIG. 4 ). Insuch examples, the memory system may perform adjustment 525-a (e.g., thememory system may shift one or more thresholds to the left), anadjustment 525-b (e.g., the memory system may shift one or morethresholds to the right), a combination thereof as described withreference to FIG. 4 .

In some examples, the system 500 may include one or more additionalcounters 515. For example, the system 500 may include a counter 515 foreach read threshold as described with reference to FIG. 4 (e.g., forMLC, the system 500 may include 3 counters 515). In some such examples,the system may not include logic circuitry 540 (e.g., each counter 515may be incremented if a 1 or a 0 is read for a respective readthreshold). In such cases where the read thresholds are treatedseparately, the comparison component 520 may perform operationsdescribed with reference to FIG. 4 . For example, the comparisoncomponent 520 may iteratively adjust the values of the counters 515 toobtain accurate excess counts for each counter 515 and perform anadjustment 525-a or 525-b on a per-threshold basis, among otherexamples.

FIG. 6 illustrates a plot 600 of example read distributions that supportread threshold adjustment techniques for memory in accordance withexamples as disclosed herein. The plot 600 may be an example ofoperations implemented by a system 100 as described with reference toFIG. 1 . The plot 600 may implement aspects of the plots and systemsdescribed herein, such as the plot 400 and system 500 as described withreference to FIGS. 4 and 5 , respectively. Generally, the plot 600 mayillustrate example distributions 615 for TLC data in a memory array. Asan illustrative example, the plot 600 shows thresholds 620 anddistributions 615 for memory cells storing three bits on three levels,although aspects of the teachings herein may be extended to memory cellseach storing any quantity of bits.

The plot 600 may include a read threshold 620-a, a read threshold 620-b,a read threshold 620-c, a read threshold 620-d, a read threshold 620-e,a read threshold 620-f and a read threshold 620-g, which may be examplesof voltage thresholds, though current thresholds or charge thresholdsmay additional or alternatively be used. A memory system may read memorycells using the read thresholds 620. For example, the memory system maycompare a voltage of a signal generated in response to reading a memorycell to the read thresholds 620 and identify a logic value in responseto comparing the voltage.

In some examples, the different thresholds 620 may be associated withrespective bits stored in the memory cell. As an example of a TLC memorycell storing three bits, the threshold 620-d may be associated with arespective first bit of the memory cell, which may be referred to as a“lower bit” or a “lower page bit” of the memory cell. In some cases, thethreshold 620-d may be referred to as a “lower page threshold” or a“lower level threshold.” The threshold 620-b and the threshold 620-f maybe associated with a respective second bit of the memory cell, which maybe referred to as an “upper bit” or an “upper page bit” of the memorycell. In some cases, the thresholds 620-b and 620-f may be referred toas “upper page thresholds” or “upper level thresholds.” The thresholds620-a, 620-c, 620-e, and 620-g may be associated with a respective thirdbit of the memory cell, which may be referred to as an “extra bit” or an“extra page bit” of the memory cell. In some cases, the thresholds620-a, 620-c, 620-e, and 620-g may be referred to as “extra pagethresholds” or “extra level thresholds.” Additionally or alternatively,the lower level may be referred to as a first level, the upper level maybe referred to as a second level, and the extra level may be referred toas a third level.

Although shown as each distribution 615 corresponding to a set of threebits (e.g., the distribution 615-a corresponding to a lower page, upperpage, and extra page bits of 1, 1, and 1, respectively), it is to beunderstood that any layout or orientation of bits and distributions maybe used. In some examples, the logic values, distributions 615, and readthresholds 620 may be different than described (e.g., distributions 615and read thresholds 620 may be associated with different logic values,lower page bits, or upper page bits). Although shown as parabolic curvesfor illustrative clarity, it is to be understood that the distributions615 may be any shape or associated with any logic value.

In the example shown, if a voltage signal of a memory cell is less thanthe threshold 620-d the memory cell may read the respective first bit(e.g., lower page bit) as a 1. The memory system may read the respectivesecond bit (e.g., upper page bit) using the read threshold 620-b if therespective first bit is 1. For example, the memory system may read thesecond bit as a 1 if the voltage signal is less than the threshold 620-band a 0 if the voltage signal is greater than the threshold 620-b. Thememory system may read the respective third bit (e.g., extra page bit)using the read threshold 620-a if the respective second bit is 1. Forexample, the memory system may read the third bit as a 1 if the voltagesignal is less than the threshold 620-a and a 0 if the signal is greaterthan the thresholds 620-a.

In some examples, one or more of the distributions 615 may becomeshifted over time such that the one or more read thresholds 620 deviatefrom an ideal read threshold, which may result in one or more errors inthe data as described herein. Accordingly, the memory system may adjustone or more read thresholds 620 using one or more counters.

In some examples, for multi-bit cells (e.g., MLC, TLC, QLC, etc.)configured to store two or more bits of information, the memory systemmay implement multiple counters. In the example of a TLC cell shown inFIG. 6 , in some cases the memory system may use a set of countersassociated with each level of the memory cells. For example, a firstcounter may correspond to the first level (e.g., read threshold 620-d),a second counter may correspond to the second level (e.g., readthresholds 620-b and 620-f), and a third counter may correspond to thethird level (e.g., read thresholds 620-a, 620-c, 620-e, and 620-g).

The memory system may use an algorithm as described herein withreference to FIG. 4 , but extended and adapted to accommodate anadditional level, to increment the counters and determine a direction,magnitude, or both to adjust the read thresholds 620 using a linearcombination of the three counters. For example, the memory system mayincrement the first counter to track a quantity of memory cells storinga lower page bit logic value of 1 to obtain the lower page excess 1s.The memory system may increment the second counter using a logic gate asdescribed herein (e.g., a XOR or XNOR logic gate). By using a logicgate, the second counter may indicate a quantity of cells storing anupper bit logic value to the right (or left) of the thresholds 620-b and620-f. Similarly, the memory system may increment the third counter suchthat the third counter indicates a quantity of cells storing an extrabit logic value to the right (or left) of the thresholds 620-a, 620-c,620-e, and 620-g. The memory system may obtain a first count associatedwith the first counter indicating excess is of the lower level, a secondcount associated with a second counter indicating excess is in the upperlevel, and a third count associated with the third counter indicatingexcess is in the extra level. For example, the memory system may performa linear combination of the values indicated by the counters which willindicate the total number of excess is across all of the bit levels. Forexample, the first count may be the value of the counter, the secondcount may be the value of the second counter multiplied by two, a thirdcount may be the value of a third counter multiplied by four, and so on.The resulting value (e.g., the linear combination) may be used todetermine which direction or magnitude to shift all of the thresholds620. Although described as using a linear combination for a total count,it is to be understood any technique may be used to evaluate the valuesindicated by the counters associated with each level of the memorycells.

Additionally or alternatively, the memory system may use a set ofcounters respectively associated with a set of read thresholds 620. Inother words, each counter of the set of counters may correspond to arespective read threshold 620 of the set of read thresholds 620 (e.g.,the memory system may use seven counters in plot 600 for TLC memorycells). The memory system may adjust the count of each counteriteratively as described herein with reference to FIG. 4 . For example,the memory system may determine an edge read threshold 620-a count (or acount of the other edge read threshold 620-g). The edge threshold countsmay be accurate because any bits incorrectly read are lost to the nextdistribution or gained from the next distribution (e.g., an accuratequantity of excess 1s or 0s may be obtained due to a single source ofextra 1s or 0s). The memory system may use the count of the edge readthresholds to obtain an accurate count for the next read thresholds 620.For example, the memory system may subtract excess is of the counter forthe read threshold 620-a from the counter of the read threshold 620-b.By accounting for the excess (or dearth) of logic values from the edgethreshold, an accurate count may be obtained for the counter of the readthreshold 620-b. The memory system may iterate such procedures for eachread threshold 62, which may enable the memory system to treat each readthreshold 620 separately (e.g., the memory system may use eachindividual adjusted count to select a direction or magnitude ofadjustment for each read threshold 620).

In some examples, the memory system may determine counts for eachcounter in the set of counters (e.g., each counter that corresponds to arespective read threshold 620) based on a subset of memory cells. Forexample, each read threshold 620 may correspond to a different logicvalue for one of multiple levels in a memory cell. That is, for arespective read threshold 620, a single level of a memory cell maychange logic value depending on which side of the read threshold 620 thevoltage lies (e.g., the other levels of the cell may not change logicvalue for the read threshold 620). In other words, the other levels ofthe memory cell may be constant and one of the levels may be changeablewhen moving across the read threshold 620. In some such examples, thememory system may select a subset of memory cells to determine a countfor a counter that corresponds to a respective read threshold 620. Forexample, the memory system may analyze (e.g., look at) memory cells thathave one or more levels with logic values that are constant for therespective read threshold 620. The memory system may determine a countof the subset of memory cells that have a first logic value or a secondlogic value for the level that is not constant with respective to theread threshold 620. As an illustrative example, for the read threshold620-b, the lower bit and the extra bit may be a same value of 1 and 0,respectively, regardless of whether the voltage lies on the left orright of the read threshold 620-b. The memory system may select memorycells that have a lower bit value of 1 and an extra bit value of 0 todetermine the count associated with the read threshold 620-b. Forexample, the memory system may determine how many upper bits have afirst logic value (e.g., 1 or 0) from the subset of memory cells with alower bit value of 1 and an extra bit value of 0. In some cases, thememory system may perform such counts for each counter (e.g., each readthreshold 620) and adjust the counts as described herein (e.g., usingthe edge threshold counts and adjusting each count iteratively).

While shown as three bits per cell for illustrative clarity, it is to beunderstood that the concepts described herein with reference to FIG. 6and elsewhere may be extended and implemented for other cell typesstoring any quantity of bits (e.g., other multi-bit cells, such as QLC).

FIG. 7 illustrates an example of a system 700 that supports readthreshold adjustment techniques for memory in accordance with examplesas disclosed herein. In some examples, the system 700 may be an exampleof or include aspects of the systems and plots as described withreference to FIGS. 1-6 . For example, the system 700 may include memory705, which may be example of a memory array as described herein (e.g.,an array of NAND multi-bit memory cells). The system 700 may illustratean example implementation of adjusting a read threshold using a decoder710, one or more counters 715, and a comparison component 720. Althoughshown as separate for illustrative clarity, the various components ofthe system 700 may be combined or located different than shown (e.g.,the decoder 710 may include the counters 715 and the comparisoncomponent 720 in logic).

In some examples, the system 700 may include an encoder 735. The encoder735 may be an example of an encoder as described herein (e.g., anencoder 335). For example, the encoder 735 may be configured to scrambleuser data into a codeword as described herein with reference to FIGS.2-6 . For example, the encoder 735 may receive user data and generate abalanced sequence of 0's and 1's using a scrambler. The encoder 735 mayadditionally or alternatively be configured to encode the codeword inresponse to an ECC code, to support an error detection or correctionprocedure if later reading the codeword from the memory 705.

The system 700 may show a data path for performing one or moreadjustments 725 of one or more read thresholds using the techniquesdescribed herein, including with reference to FIG. 6 . For example, data(e.g., a codeword) may be read from the memory 705. The data may beinput to the decoder 710. The data may also be input to the counter715-a, the counter 715-b, and the counter 715-c. The counters 715 may beexamples of a first counter, second counter, and third counter asdescribed with reference to FIG. 6 .

The decoder 710 may detect an uncorrectable error 730 in response todecoding the data. Additionally or alternatively, the error 730 may be aquantity of errors that satisfy a threshold (e.g., the memory system mayadjust read thresholds if the quantity of errors satisfies a thresholdeven if the errors are correctable). In some examples, the decoder 710may include a descrambler in addition or in the alternative to the ECCdecoder. For example, the decoder 710 may be configured to descramblethe codeword to the original user data as part of the read operation.Additionally or alternatively, the counters 715 may track a quantity ofbits in the data that correspond to a first logic value (e.g., thecounters 715 may increment each time a 1 or a 0 is read from arespective first bit, a respective second bit, or a respective third bitof a memory cell) or a quantity of memory cells that correspond to afirst result output by a set of logic circuitry (e.g., the counter 715-band/or the counter 715-c may increment each time the logic circuitryoutputs a first result or a second result, such as a XOR or XNOR resultof the three bits) as described herein, including with reference toFIGS. 4 and 6 .

In some examples, the system 700 may include logic circuitry 740. Thelogic circuitry 740 may be configured to perform any of the operationsascribed herein to logic circuitry or logic gates in connection withadjusting one or more read thresholds. For example, the logic circuitry740-a may include a logic gate (e.g., an XNOR logic gate) configured toreceive one or more inputs (e.g., a respective upper bit and arespective lower bit read from each memory cell) and output acorresponding result (e.g., a 1 to the counter 715-b) indicating whetherthe two inputs are the same or different, among other possibilities. Thelogic circuitry 740-b may include a logic gate (e.g., a XOR logic gate)configured to receive one or more inputs (e.g., a respective upper bit,a respective lower bit, and a respective extra bit read from each memorycell) and output a corresponding result (e.g., a 1 to the counter 715-c)indicating whether the two inputs are the same or different, among otherpossibilities.

The comparison component 720 may receive an indication of a quantity ofbits from the one or more counters 715, an indication that the dataincludes an uncorrectable error 730 from the decoder 710, or anycombination thereof. For example, if the decoder 710 detects that theerrors 730 in the data are uncorrectable (e.g., the data includes anuncorrectable quantity of errors for an ECC scheme), the decoder 710 mayindicate the error 730 to the comparison component 720. The comparisoncomponent 720 may compare the quantity of bits to a second quantity ofbits (e.g., a quantity of 0s to a quantity of 1s) or a threshold asdescribed herein, including with reference to FIG. 4 . Additionally oralternatively, the comparison component 720 or another component maydetermine a linear combination of the first counter 715-a and thecounter 715-b and use the result to determine the direction or magnitudeof an adjustment 725, as described with reference to FIGS. 4 and 6 .

The memory system may perform an adjustment 725 in response to a resultfrom the comparison component 720. For example, if the comparisoncomponent 720 indicates that the read thresholds are relatively too farfrom an ideal read threshold location as described herein, the memorysystem may select a direction of adjustment, a magnitude of adjustment,or both in accordance with the magnitude and direction of the count(e.g., to reduce the quantity of bits being incorrectly read as part ofanother distribution due to a current location of the read thresholds,among other examples as described herein with reference to FIG. 4 ). Insuch examples, the memory system may perform adjustment 725-a (e.g., thememory system may shift one or more thresholds to the left), anadjustment 725-b (e.g., the memory system may shift one or morethresholds to the right), a combination thereof as described withreference to FIGS. 4 and 6 .

In some examples, the system 700 may include one or more additionalcounters 715. For example, the system 700 may include a counter 715 foreach read threshold as described with reference to FIG. 4 or 6 (e.g.,for TLC, the system 700 may include 7 counters 715). In some suchexamples, the system may not include logic circuitry 740 (e.g., eachcounter 715 may be incremented if a 1 or a 0 is read for a respectiveread threshold). In such cases where the read thresholds are treatedseparately, the comparison component 720 may perform operationsdescribed with reference to FIGS. 4 and 6 . For example, the comparisoncomponent 720 may iteratively adjust the values of the counters 715 toobtain accurate excess counts for each counter 715 and perform anadjustment 725-a or 725-b on a per-threshold basis, among otherexamples.

FIG. 8 illustrates an example of a block diagram 800 that supports readthreshold adjustment techniques for memory in accordance with examplesas disclosed herein. The memory system 805 may be an example of aspectsof a memory system as described with reference to FIGS. 1-7 . In someexamples, the memory system 805 may be referred to as a memory device ormay include one or more memory devices. The memory system 805 mayinclude a read component 810, a counter component 815, an errorcomponent 820, a read threshold component 825, a comparison component830, a selection component 835, and an adjustment component 840. Each ofthese modules may communicate, directly or indirectly, with one another(e.g., via one or more buses).

The read component 810 may be configured as or otherwise support a meansfor reading a codeword from a memory array of one or more memory devicesusing a read threshold having a first value. The counter component 815may be configured as or otherwise support a means for incrementing acounter of the one or more memory devices in response to reading thecodeword, the counter indicating a quantity of bits of the codeword thatcorrespond to a first logic value. The error component 820 may beconfigured as or otherwise support a means for detecting an error in thecodeword after reading the codeword. The read threshold component 825may be configured as or otherwise support a means for adjusting the readthreshold from the first value to a second value in response to thequantity of bits indicated by the counter. The read component 810 may beconfigured as or otherwise support a means for reading the codeword fromthe memory array using the read threshold having the second value.

The comparison component 830 may be configured as or otherwise support ameans for comparing the quantity of bits of the codeword that correspondto the first logic value to a second quantity of bits of the codewordthat correspond to a second logic value, where adjusting the readthreshold from the first value to the second value is in response to thecomparison. In some examples, the selection component 835 may beconfigured as or otherwise support a means for selecting a direction ofadjustment, a magnitude of adjustment, or both associated with adjustingthe read threshold in response to the comparison. In some examples, theread threshold component 825 may be configured as or otherwise support ameans for adjusting the read threshold from the first value to thesecond value in accordance with the selected direction of adjustment,the magnitude of adjustment, or both.

In some examples, the comparison component 830 may be configured as orotherwise support a means for determining that the quantity of bits ofthe codeword that correspond to the first logic value satisfies athreshold in response to the comparing. The selection component 835 maybe configured as or otherwise support a means for selecting a directionof adjustment, a magnitude of adjustment, or both associated withadjusting the read threshold in response to the quantity of bitssatisfying the threshold.

In some examples, the read threshold component 825 may be configured asor otherwise support a means for adjusting the read threshold by amagnitude, a direction, or both corresponding to the quantity of bitsindicated by the counter.

The error component 820 may be configured as or otherwise support ameans for determining that the error is an uncorrectable error for anerror correction code scheme, where detecting the error is in responseto the error correction code scheme, and where adjusting the readthreshold is in response to the error being uncorrectable for the errorcorrection code scheme.

In some examples, the read threshold includes a voltage threshold, acurrent threshold, a charge threshold, or any combination thereof.

In some examples, the error component 820 may be configured as orotherwise support a means for detecting a second error in the codewordbased at least in part on reading the codeword using the read thresholdhaving the second value. The read threshold component 825 may beconfigured as or otherwise support a means for adjusting the readthreshold from the second value to a third value on the detected seconderror.

In some examples, the read component 810 may be configured as orotherwise support a means for reading data from a set of memory cellswithin the one or more memory devices using at least three readthresholds, each memory cell of the set of memory cells configured tostore a respective plurality of bits each corresponding to a respectivelevel of a plurality of levels each corresponding to a respective subsetof read thresholds of the at least three read thresholds. The countercomponent 815 may be configured as or otherwise support a means forincrementing each counter of a set of counters based at least in part onreading the data, the set of counters including a first countercorresponding to a first level of the plurality of levels and a secondcounter corresponding to a second level of the plurality of levels. Theerror component 820 may be configured as or otherwise support a meansfor detecting an error in the data based at least in part on reading thedata using the at least three read thresholds. The read thresholdcomponent 825 may be configured as or otherwise support a means foradjusting one or more of the at least three read thresholds based atleast in part on the set of counters. In some examples, the readcomponent 810 may be configured as or otherwise support a means forreading the data from the memory array after adjusting the one or moreof the at least three read thresholds.

In some examples, to support incrementing each counter of the set ofcounters, the counter component 815 may be configured as or otherwisesupport a means for incrementing the first counter corresponding to thefirst level, the first counter indicating a quantity of bits stored bythe set of memory cells that correspond to a first logic value. In someexamples, to support incrementing each counter of the set of counters,the counter component 815 may be configured as or otherwise support ameans for incrementing the second counter corresponding to the secondlevel, the second counter indicating a quantity of outputs from one ormore logic gates corresponding to a particular logic value.

In some examples, the inputs to the one or more logic gates include afirst bit stored by a first memory cell and a second bit stored by thefirst memory cell, the first bit corresponding to the first level andthe second bit corresponding to the second level.

In some examples, to support incrementing each counter of the set ofcounters, the counter component 815 may be configured as or otherwisesupport a means for incrementing a third counter corresponding to athird level of the plurality of levels, the third counter indicating asecond quantity of outputs from the one or more logic gatescorresponding to a particular logic value, where the inputs to the oneor more logic gates include a first bit stored by a first memory cell, asecond bit stored by the first memory cell, and a third bit stored bythe first memory cell. In some examples, to support incrementing eachcounter of the set of counters, the counter component 815 may beconfigured as or otherwise support a means for where the first bitcorresponds to the first level, the second bit corresponds to the secondlevel, and the third bit corresponds to the third level.

In some examples, the counter component 815 may be configured as orotherwise support a means for determining a quantity of bits thatcorrespond to a first logic value based at least in part on acombination of counts, each of the counts indicated by a respectivecounter of the set of counters. In some examples, the combination ofcounts includes a linear combination of a first count indicated by thefirst counter, a second count indicated by the second counter, a thirdcount indicated by a third counter, a fourth count indicated by a fourthcounter, or any combination thereof.

In some examples, a direction, a magnitude, or both of the adjusting ofthe at least three read thresholds is based at least in part on thequantity of bits that correspond to the first logic value. In someexamples, to support adjusting, the read threshold component 825 may beconfigured as or otherwise support a means for adjusting the at leastthree read thresholds in a direction indicated by the set of counters.In some examples, to support adjusting, the read threshold component 825may be configured as or otherwise support a means for adjusting the atleast three read thresholds by a magnitude indicated by the set ofcounters.

In some examples, the selection component 835 may be configured as orotherwise support a means for selecting a direction of adjustment, amagnitude of adjustment, or both associated with the adjusting of theone or more of the at least three read thresholds based at least in parton the set of counters.

In some examples, the error component 820 may be configured as orotherwise support a means for detecting a second error in the data basedat least in part on reading the data from the memory array afteradjusting the one or more of the at least three read thresholds. In someexamples, the read threshold component 825 may be configured as orotherwise support a means for readjusting the one or more of the atleast three read thresholds based at least in part on detecting thesecond error. In some examples, the at least three read thresholds eachinclude a respective voltage threshold, a respective current threshold,or any combination thereof.

In some examples, the read component 810 may be configured as orotherwise support a means for reading data from a set of memory cellswithin the one or more memory devices using at least three readthresholds, each memory cell of the set of memory cells configured tostore at least two bits. In some examples, the counter component 815 maybe configured as or otherwise support a means for incrementing eachcounter of a set of counters based at least in part on reading the datausing the at least three read thresholds, where each counter of the setof counters corresponds to a respective read threshold of the at leastthree read thresholds and indicates a respective quantity of bits of thedata corresponding to a first logic value. The adjustment component 840may be configured as or otherwise support a means for adjusting a firstquantity indicated by a first counter of the set of counters using asecond quantity indicated by a second counter of the set of counters. Insome examples, the read threshold component 825 may be configured as orotherwise support a means for adjusting, after adjusting the firstquantity indicated by the first counter, one or more of the at leastthree read thresholds based at least in part on the set of counters. Insome examples, the read component 810 may be configured as or otherwisesupport a means for reading the data from the memory array afteradjusting the one or more of the at least three read thresholds.

In some examples, the counter component 815 may be configured as orotherwise support a means for determining the first quantity indicatedby the first counter, the first quantity indicating a quantity of bitsfor a first respective threshold of the at least three read thresholdsthat correspond to the first logic value. In some examples, the countercomponent 815 may be configured as or otherwise support a means fordetermining the second quantity indicated by the second counter, thesecond quantity indicating a quantity of bits for a second respectivethreshold of the at least three read thresholds that correspond to thefirst logic value.

In some examples, to support adjusting the first quantity, theadjustment component 840 may be configured as or otherwise support ameans for subtracting the second quantity from the first quantity. Insome examples, the adjustment component 840 may be configured as orotherwise support a means for adjusting a third quantity indicated by athird counter of the set of counters based at least in part on the firstquantity, the second quantity, or both.

In some examples, the read threshold component 825 may be configured asor otherwise support a means for adjusting a first threshold of the atleast three read thresholds in a direction indicated by the firstcounter, a second threshold of the at least three read thresholds in adirection indicated by the second counter, a third threshold of the atleast three read thresholds in a direction indicated by a third counter,a fourth threshold of the at least three read thresholds in a directionindicated by a fourth counter, or any combination thereof.

In some examples, the read threshold component 825 may be configured asor otherwise support a means for adjusting a first threshold of the atleast three read thresholds by a magnitude indicated by the firstcounter, a second threshold of the at least three read thresholds by amagnitude indicated by the second counter, a third threshold of the atleast three read thresholds by a magnitude indicated by a third counter,a fourth threshold of the at least three read thresholds by a magnitudeindicated by a fourth counter, or any combination thereof.

In some examples, the read threshold component 825 may be configured asor otherwise support a means for selecting a subset of memory cells fromthe set of memory cells for each read threshold of the at least threeread thresholds, where a respective subset of memory cells correspondsto a respective read threshold and a respective counter, andincrementing the respective counter based on a quantity of therespective subset of memory cells that correspond to the first logicstate.

FIG. 9 shows a flowchart illustrating a method 900 that supports readthreshold adjustment techniques for memory in accordance with examplesas disclosed herein. The operations of method 900 may be implemented bya memory system or its components as described herein. For example, theoperations of method 900 may be performed by a memory system asdescribed with reference to FIGS. 1 through 8 . In some examples, amemory system may execute a set of instructions to control thefunctional elements of the device to perform the described functions.Additionally or alternatively, the memory system may perform aspects ofthe described functions using special-purpose hardware.

At 905, the method may include reading a codeword from a memory array ofone or more memory devices using a read threshold having a first value.The operations of 905 may be performed in accordance with examples asdisclosed herein. In some examples, aspects of the operations of 905 maybe performed by a read component 810 as described with reference to FIG.8 .

At 910, the method may include incrementing a counter based at least inpart on reading the codeword, the counter indicating a quantity of bitsof the codeword that correspond to a first logic value. The operationsof 910 may be performed in accordance with examples as disclosed herein.In some examples, aspects of the operations of 910 may be performed by acounter component 815 as described with reference to FIG. 8 .

At 915, the method may include detecting an error in the codeword afterreading the codeword. The operations of 915 may be performed inaccordance with examples as disclosed herein. In some examples, aspectsof the operations of 915 may be performed by an error component 820 asdescribed with reference to FIG. 8 .

At 920, the method may include adjusting the read threshold from thefirst value to a second value based at least in part on the quantity ofbits indicated by the counter. The operations of 920 may be performed inaccordance with examples as disclosed herein. In some examples, aspectsof the operations of 920 may be performed by a read threshold component825 as described with reference to FIG. 8 .

At 925, the method may include reading the codeword from the memoryarray using the read threshold having the second value. The operationsof 925 may be performed in accordance with examples as disclosed herein.In some examples, aspects of the operations of 925 may be performed by aread component 810 as described with reference to FIG. 8 .

In some examples, an apparatus as described herein may perform a methodor methods, such as the method 900. The apparatus may include, features,circuitry, logic, means, or instructions (e.g., a non-transitorycomputer-readable medium storing instructions executable by a processor)for reading a codeword from a memory array of the one or more memorydevices using a read threshold having a first value, incrementing acounter based at least in part on reading the codeword, the counterindicating a quantity of bits of the codeword that correspond to a firstlogic value, detecting an error in the codeword after reading thecodeword, adjusting the read threshold from the first value to a secondvalue based at least in part on the quantity of bits indicated by thecounter, and reading the codeword from the memory array using the readthreshold having the second value.

Some examples of the method 900 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for comparing the quantity of bits of the codeword thatcorrespond to the first logic value to a second quantity of bits of thecodeword that correspond to a second logic value, where adjusting theread threshold from the first value to the second value may be based atleast in part on the comparison.

Some examples of the method 900 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for selecting a direction of adjustment, a magnitude ofadjustment, or both associated with adjusting the read threshold basedat least in part on the comparison.

Some examples of the method 900 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for adjusting the read threshold from the first value tothe second value in accordance with the selected direction ofadjustment, the magnitude of adjustment, or both.

Some examples of the method 900 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for determining that the quantity of bits of the codewordthat correspond to the first logic value satisfies a threshold based atleast in part on the comparing and selecting a direction of adjustment,a magnitude of adjustment, or both associated with adjusting the readthreshold based at least in part on the quantity of bits satisfying thethreshold.

Some examples of the method 900 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for adjusting the read threshold may include operations,features, circuitry, logic, means, or instructions for adjusting theread threshold by a magnitude, a direction, or both corresponding to thequantity of bits indicated by the counter.

Some examples of the method 900 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for determining that the error may be an uncorrectableerror for an error correction code scheme, where detecting the error maybe based at least in part on the error correction code scheme, and whereadjusting the read threshold may be based at least in part on the errorbeing uncorrectable for the error correction code scheme.

In some examples of the method 900 and the apparatus described herein,the read threshold may be a voltage threshold, a current threshold, acharge threshold or any combination thereof.

Some examples of the method 900 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for detecting a second error in the codeword based at leastin part on reading the codeword using the read threshold having thesecond value and adjusting the read threshold from the second value to athird value based at least in part on the detected second error.

FIG. 10 shows a flowchart illustrating a method 1000 that supports readthreshold adjustment techniques for memory in accordance with examplesas disclosed herein. The operations of method 1000 may be implemented bya memory system or its components as described herein. For example, theoperations of method 1000 may be performed by a memory system asdescribed with reference to FIGS. 1 through 8 . In some examples, amemory system may execute a set of instructions to control thefunctional elements of the device to perform the described functions.Additionally or alternatively, the memory system may perform aspects ofthe described functions using special-purpose hardware.

At 1005, the method may include reading data from a set of memory cellswithin one or more memory devices using at least three read thresholds,each memory cell of the set of memory cells configured to store arespective plurality of bits each corresponding to a respective level ofa plurality of levels each corresponding to a respective subset of readthresholds of the at least three read thresholds. The operations of 1005may be performed in accordance with examples as disclosed herein. Insome examples, aspects of the operations of 1005 may be performed by aread component 810 as described with reference to FIG. 8 .

At 1010, the method may include incrementing each counter of a set ofcounters based at least in part on reading the data, the set of countersincluding a first counter corresponding to a first level of theplurality of levels and a second counter corresponding to a second levelof the plurality of levels. The operations of 1010 may be performed inaccordance with examples as disclosed herein. In some examples, aspectsof the operations of 1010 may be performed by a counter component 815 asdescribed with reference to FIG. 8 .

At 1015, the method may include detecting an error in the data based atleast in part on reading the data using the at least three readthresholds. The operations of 1015 may be performed in accordance withexamples as disclosed herein. In some examples, aspects of theoperations of 1015 may be performed by an error component 820 asdescribed with reference to FIG. 8 .

At 1020, the method may include adjusting one or more of the at leastthree read thresholds based at least in part on the set of counters. Theoperations of 1020 may be performed in accordance with examples asdisclosed herein. In some examples, aspects of the operations of 1020may be performed by a read threshold component 825 as described withreference to FIG. 8 .

At 1025, the method may include reading the data from the memory arrayafter adjusting the one or more of the at least three read thresholds.The operations of 1025 may be performed in accordance with examples asdisclosed herein. In some examples, aspects of the operations of 1025may be performed by a read component 810 as described with reference toFIG. 8 .

In some examples, an apparatus as described herein may perform a methodor methods, such as the method 1000. The apparatus may include,features, circuitry, logic, means, or instructions (e.g., anon-transitory computer-readable medium storing instructions executableby a processor) for reading data from a set of memory cells within theone or more memory devices using at least three read thresholds, eachmemory cell of the set of memory cells configured to store a respectiveplurality of bits each corresponding to a respective level of aplurality of levels each corresponding to a respective subset of readthresholds of the at least three read thresholds, incrementing eachcounter of a set of counters based at least in part on reading the data,the set of counters including a first counter corresponding to a firstlevel of the plurality of levels and a second counter corresponding to asecond level of the plurality of levels, detecting an error in the databased at least in part on reading the data using the at least three readthresholds, adjusting one or more of the at least three read thresholdsbased at least in part on the set of counters, and reading the data fromthe memory array after adjusting the one or more of the at least threeread thresholds.

In some examples of the method 1000 and the apparatus described herein,operations, features, circuitry, logic, means, or instructions forincrementing each counter of the set of counters may include operations,features, circuitry, logic, means, or instructions for incrementing thefirst counter corresponding to the first level, the first counterindicating a quantity of bits stored by the set of memory cells thatcorrespond to a first logic value, and incrementing the second countercorresponding to the second level, the second counter indicating aquantity of outputs from one or more logic gates corresponding to aparticular logic value.

In some examples of the method 1000 and the apparatus described herein,the inputs to the one or more logic gates include a first bit stored bya first memory cell and a second bit stored by the first memory cell,the first bit corresponding to the first level and the second bitcorresponding to the second level.

In some examples of the method 1000 and the apparatus described herein,operations, features, circuitry, logic, means, or instructions forincrementing each counter of the set of counters may include operations,features, circuitry, logic, means, or instructions for incrementing athird counter corresponding to a third level of the plurality of levels,the third counter indicating a second quantity of outputs from the oneor more logic gates corresponding to a particular logic value, where theinputs to the one or more logic gates include a first bit stored by afirst memory cell, a second bit stored by the first memory cell, and athird bit stored by the first memory cell, and where the first bitcorresponds to the first level, the second bit corresponds to the secondlevel, and the third bit corresponds to the third level.

Some examples of the method 1000 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for determining a quantity of bits that correspond to afirst logic value based at least in part on a combination of counts,each of the counts indicated by a respective counter of the set ofcounters.

In some examples of the method 1000 and the apparatus described herein,the combination of counts includes a linear combination of a first countindicated by the first counter, a second count indicated by the secondcounter, a third count indicated by a third counter, a fourth countindicated by a fourth counter, or any combination thereof.

In some examples of the method 1000 and the apparatus described herein,a direction, a magnitude, or both of the adjusting of the at least threeread thresholds may be based at least in part on the quantity of bitsthat correspond to the first logic value.

In some examples of the method 1000 and the apparatus described herein,operations, features, circuitry, logic, means, or instructions for theadjusting may include operations, features, circuitry, logic, means, orinstructions for adjusting the at least three read thresholds in adirection indicated by the set of counters.

In some examples of the method 1000 and the apparatus described herein,operations, features, circuitry, logic, means, or instructions for theadjusting may include operations, features, circuitry, logic, means, orinstructions for adjusting the at least three read thresholds by amagnitude indicated by the set of counters.

Some examples of the method 1000 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for selecting a direction of adjustment, a magnitude ofadjustment, or both associated with the adjusting of the one or more ofthe at least three read thresholds based at least in part on the set ofcounters.

Some examples of the method 1000 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for detecting a second error in the data based at least inpart on reading the data from the memory array after adjusting the oneor more of the at least three read thresholds and readjusting the one ormore of the at least three read thresholds based at least in part ondetecting the second error.

In some examples of the method 1000 and the apparatus described herein,the at least three read thresholds each include a respective voltagethreshold, a respective current threshold, or any combination thereof.

FIG. 11 shows a flowchart illustrating a method 1100 that supports readthreshold adjustment techniques for memory in accordance with examplesas disclosed herein. The operations of method 1100 may be implemented bya memory system or its components as described herein. For example, theoperations of method 1100 may be performed by a memory system asdescribed with reference to FIGS. 1 through 8 . In some examples, amemory system may execute a set of instructions to control thefunctional elements of the device to perform the described functions.Additionally or alternatively, the memory system may perform aspects ofthe described functions using special-purpose hardware.

At 1105, the method may include reading data from a set of memory cellswithin one or more memory devices using at least three read thresholds,each memory cell of the set of memory cells configured to store at leasttwo bits. The operations of 1105 may be performed in accordance withexamples as disclosed herein. In some examples, aspects of theoperations of 1105 may be performed by a read component 810 as describedwith reference to FIG. 8 .

At 1110, the method may include incrementing each counter of a set ofcounters based at least in part on reading the data using the at leastthree read thresholds, where each counter of the set of counterscorresponds to a respective read threshold of the at least three readthresholds and indicates a respective quantity of bits of the datacorresponding to a first logic value. The operations of 1110 may beperformed in accordance with examples as disclosed herein. In someexamples, aspects of the operations of 1110 may be performed by acounter component 815 as described with reference to FIG. 8 .

At 1115, the method may include adjusting a first quantity indicated bya first counter of the set of counters using a second quantity indicatedby a second counter of the set of counters. The operations of 1115 maybe performed in accordance with examples as disclosed herein. In someexamples, aspects of the operations of 1115 may be performed by anadjustment component 840 as described with reference to FIG. 8 .

At 1120, the method may include adjusting, after adjusting the firstquantity indicated by the first counter, one or more of the at leastthree read thresholds based at least in part on the set of counters. Theoperations of 1120 may be performed in accordance with examples asdisclosed herein. In some examples, aspects of the operations of 1120may be performed by a read threshold component 825 as described withreference to FIG. 8 .

At 1125, the method may include reading the data from the memory arrayafter adjusting the one or more of the at least three read thresholds.The operations of 1125 may be performed in accordance with examples asdisclosed herein. In some examples, aspects of the operations of 1125may be performed by a read component 810 as described with reference toFIG. 8 .

In some examples, an apparatus as described herein may perform a methodor methods, such as the method 1100. The apparatus may include,features, circuitry, logic, means, or instructions (e.g., anon-transitory computer-readable medium storing instructions executableby a processor) for reading data from a set of memory cells within theone or more memory devices using at least three read thresholds, eachmemory cell of the set of memory cells configured to store at least twobits, incrementing each counter of a set of counters based at least inpart on reading the data using the at least three read thresholds, whereeach counter of the set of counters corresponds to a respective readthreshold of the at least three read thresholds and indicates arespective quantity of bits of the data corresponding to a first logicvalue, adjusting a first quantity indicated by a first counter of theset of counters using a second quantity indicated by a second counter ofthe set of counters, adjusting, after adjusting the first quantityindicated by the first counter, one or more of the at least three readthresholds based at least in part on the set of counters, and readingthe data from the memory array after adjusting the one or more of the atleast three read thresholds.

Some examples of the method 1100 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for determining the first quantity indicated by the firstcounter, the first quantity indicating a quantity of bits for a firstrespective threshold of the at least three read thresholds thatcorrespond to the first logic value, and determining the second quantityindicated by the second counter, the second quantity indicating aquantity of bits for a second respective threshold of the at least threeread thresholds that correspond to the first logic value.

In some examples of the method 1100 and the apparatus described herein,operations, features, circuitry, logic, means, or instructions foradjusting the first quantity may include operations, features,circuitry, logic, means, or instructions for subtracting the secondquantity from the first quantity.

Some examples of the method 1100 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for adjusting a third quantity indicated by a third counterof the set of counters based at least in part on the first quantity, thesecond quantity, or both.

Some examples of the method 1100 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for adjusting a first threshold of the at least three readthresholds in a direction indicated by the first counter, a secondthreshold of the at least three read thresholds in a direction indicatedby the second counter, a third threshold of the at least three readthresholds in a direction indicated by a third counter, a fourththreshold of the at least three read thresholds in a direction indicatedby a fourth counter, or any combination thereof.

Some examples of the method 1100 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for adjusting a first threshold of the at least three readthresholds by a magnitude indicated by the first counter, a secondthreshold of the at least three read thresholds by a magnitude indicatedby the second counter, a third threshold of the at least three readthresholds by a magnitude indicated by a third counter, a fourththreshold of the at least three read thresholds by a magnitude indicatedby a fourth counter, or any combination thereof.

Some examples of the method 1100 and the apparatus described herein mayfurther include operations, features, circuitry, logic, means, orinstructions for selecting a subset of memory cells from the set ofmemory cells for each read threshold of the at least three readthresholds, where a respective subset of memory cells corresponds to arespective read threshold and a respective counter, and incrementing therespective counter based on a quantity of the respective subset ofmemory cells that correspond to the first logic state.

It should be noted that the methods described above describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Further, portions from two or more of the methods may be combined.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof. Some drawings may illustrate signals as a single signal;however, the signal may represent a bus of signals, where the bus mayhave a variety of bit widths.

If used to describe a conditional action or process, the terms “if,”“when,” “based on,” “based at least in part on,” and “in response to,”may be interchangeable.

The terms “electronic communication,” “conductive contact,” “connected,”and “coupled” may refer to a relationship between components thatsupports the flow of signals between the components. Components areconsidered in electronic communication with (or in conductive contactwith or connected with or coupled with) one another if there is anyconductive path between the components that can, at any time, supportthe flow of signals between the components. At any given time, theconductive path between components that are in electronic communicationwith each other (or in conductive contact with or connected with orcoupled with) may be an open circuit or a closed circuit based on theoperation of the device that includes the connected components. Theconductive path between connected components may be a direct conductivepath between the components or the conductive path between connectedcomponents may be an indirect conductive path that may includeintermediate components, such as switches, transistors, or othercomponents. In some examples, the flow of signals between the connectedcomponents may be interrupted for a time, for example, using one or moreintermediate components such as switches or transistors.

The term “coupling” refers to condition of moving from an open-circuitrelationship between components in which signals are not presentlycapable of being communicated between the components over a conductivepath to a closed-circuit relationship between components in whichsignals are capable of being communicated between components over theconductive path. If a component, such as a controller, couples othercomponents together, the component initiates a change that allowssignals to flow between the other components over a conductive path thatpreviously did not permit signals to flow.

The term “isolated” refers to a relationship between components in whichsignals are not presently capable of flowing between the components.Components are isolated from each other if there is an open circuitbetween them. For example, two components separated by a switch that ispositioned between the components are isolated from each other if theswitch is open. If a controller isolates two components, the controlleraffects a change that prevents signals from flowing between thecomponents using a conductive path that previously permitted signals toflow.

The devices discussed herein, including a memory array, may be formed ona semiconductor substrate, such as silicon, germanium, silicon-germaniumalloy, gallium arsenide, gallium nitride, etc. In some examples, thesubstrate is a semiconductor wafer. In other examples, the substrate maybe a silicon-on-insulator (SOI) substrate, such as silicon-on-glass(SOG) or silicon-on-sapphire (SOP), or epitaxial layers of semiconductormaterials on another substrate. The conductivity of the substrate, orsub-regions of the substrate, may be controlled through doping usingvarious chemical species including, but not limited to, phosphorous,boron, or arsenic. Doping may be performed during the initial formationor growth of the substrate, by ion-implantation, or by any other dopingmeans.

A switching component or a transistor discussed herein may represent afield-effect transistor (FET) and comprise a three terminal deviceincluding a source, drain, and gate. The terminals may be connected toother electronic elements through conductive materials, e.g., metals.The source and drain may be conductive and may comprise a heavily-doped,e.g., degenerate, semiconductor region. The source and drain may beseparated by a lightly-doped semiconductor region or channel. If thechannel is n-type (i.e., majority carriers are electrons), then the FETmay be referred to as a n-type FET. If the channel is p-type (i.e.,majority carriers are holes), then the FET may be referred to as ap-type FET. The channel may be capped by an insulating gate oxide. Thechannel conductivity may be controlled by applying a voltage to thegate. For example, applying a positive voltage or negative voltage to ann-type FET or a p-type FET, respectively, may result in the channelbecoming conductive. A transistor may be “on” or “activated” if avoltage greater than or equal to the transistor's threshold voltage isapplied to the transistor gate. The transistor may be “off” or“deactivated” if a voltage less than the transistor's threshold voltageis applied to the transistor gate.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “exemplary” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details toproviding an understanding of the described techniques. Thesetechniques, however, may be practiced without these specific details. Insome instances, well-known structures and devices are shown in blockdiagram form to avoid obscuring the concepts of the described examples.

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations.

For example, the various illustrative blocks and modules described inconnection with the disclosure herein may be implemented or performedwith a general-purpose processor, a DSP, an ASIC, an FPGA or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general-purpose processor may be amicroprocessor, but in the alternative, the processor may be anyprocessor, controller, microcontroller, or state machine. A processormay also be implemented as a combination of computing devices (e.g., acombination of a DSP and a microprocessor, multiple microprocessors, oneor more microprocessors in conjunction with a DSP core, or any othersuch configuration).

As used herein, including in the claims, “or” as used in a list of items(for example, a list of items prefaced by a phrase such as “at least oneof” or “one or more of”) indicates an inclusive list such that, forexample, a list of at least one of A, B, or C means A or B or C or AB orAC or BC or ABC (i.e., A and B and C). Also, as used herein, the phrase“based on” shall not be construed as a reference to a closed set ofconditions. For example, an exemplary step that is described as “basedon condition A” may be based on both a condition A and a condition Bwithout departing from the scope of the present disclosure. In otherwords, as used herein, the phrase “based on” shall be construed in thesame manner as the phrase “based at least in part on.” If used todescribe a conditional action or process, the terms “if,” “when,” “basedon,” “based at least in part on,” and “in response to,” may beinterchangeable.

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media cancomprise RAM, ROM, electrically erasable programmable read-only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, digitalsubscriber line (DSL), or wireless technologies such as infrared, radio,and microwave are included in the definition of medium. Disk and disc,as used herein, include CD, laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other variations without departing fromthe scope of the disclosure. Thus, the disclosure is not limited to theexamples and designs described herein, but is to be accorded thebroadest scope consistent with the principles and novel featuresdisclosed herein.

What is claimed is:
 1. An apparatus, comprising: a memory device; and acontroller coupled with the memory device and configured to cause theapparatus to: read a plurality of memory cells of a memory array of thememory device using a read threshold having a first value; adjust theread threshold from the first value to a second value based at least inpart on a quantity of memory cells of the plurality of memory cellsindicated, by the reading using the read threshold having the firstvalue, as corresponding to a logic value of a plurality of logic values;and read the plurality of memory cells of the memory array using theread threshold having the second value.
 2. The apparatus of claim 1,wherein the controller is further configured to cause the apparatus to:compare the quantity of memory cells indicated as corresponding to thelogic value to a second quantity of memory cells of the plurality ofmemory cells indicated, by the reading using the read threshold havingthe first value, as corresponding to a second logic value of theplurality of logic values, wherein adjusting the read threshold from thefirst value to the second value is based at least in part on thecomparison.
 3. The apparatus of claim 2, wherein the controller isfurther configured to cause the apparatus to: select a direction ofadjustment, or a magnitude of adjustment, or both based at least in parton the comparison, wherein the adjusting the read threshold from thefirst value to the second value is in accordance with the selecteddirection of adjustment, or the selected magnitude of adjustment, orboth.
 4. The apparatus of claim 1, wherein the controller is furtherconfigured to cause the apparatus to: determine that the quantity ofmemory cells indicated as corresponding to the logic value satisfies athreshold, wherein adjusting the read threshold from the first value tothe second value is based at least in part on the determination that thequantity of memory cells indicated as corresponding to the logic valuesatisfies the threshold.
 5. The apparatus of claim 4, wherein thecontroller is further configured to cause the apparatus to: select adirection of adjustment, or a magnitude of adjustment, or both based atleast in part on the determination that the quantity of memory cellsindicated as corresponding to the logic value satisfies the threshold,wherein adjusting the read threshold from the first value to the secondvalue is in accordance with the selected direction of adjustment, or theselected magnitude of adjustment, or both.
 6. The apparatus of claim 1,wherein, to adjust the read threshold from the first value to the secondvalue, the controller is further configured to cause the apparatus to:determine a direction of the adjustment, or a magnitude of theadjustment, or both based at least in part on a look-up table.
 7. Theapparatus of claim 1, wherein the controller is further configured tocause the apparatus to: detect an error, using an error correction codescheme, after reading the plurality of memory cells using the readthreshold having the first value; and determine that the error is anuncorrectable error for the error correction code scheme, whereinadjusting the read threshold is based at least in part on thedetermination that the error is uncorrectable for the error correctioncode scheme.
 8. The apparatus of claim 1, wherein the read thresholdcomprises a voltage threshold, a current threshold, or a combinationthereof.
 9. The apparatus of claim 1, wherein the controller is furtherconfigured to cause the apparatus to: detect an error based at least inpart on reading the plurality of memory cells using the read thresholdhaving the second value; and adjust the read threshold from the secondvalue to a third value based at least in part on the detected error. 10.A non-transitory computer-readable medium storing code comprisinginstructions which, when executed by a processor of an electronicdevice, cause the electronic device to: read a plurality of memory cellsof a memory array using a read threshold having a first value; adjustthe read threshold from the first value to a second value based at leastin part on a quantity of memory cells of the plurality of memory cellsindicated, by the reading using the read threshold having the firstvalue, as corresponding to a logic value of a plurality of logic values;and read the plurality of memory cells of the memory array using theread threshold having the second value.
 11. The non-transitorycomputer-readable medium of claim 10, wherein the instructions, whenexecuted by the processor of the electronic device, further cause theelectronic device to: compare the quantity of memory cells indicated ascorresponding to the logic value to a second quantity of memory cells ofthe plurality of memory cells indicated, by the reading using the readthreshold having the first value, as corresponding to a second logicvalue of the plurality of logic values, wherein adjusting the readthreshold from the first value to the second value is based at least inpart on the comparison.
 12. The non-transitory computer-readable mediumof claim 11, wherein the instructions, when executed by the processor ofthe electronic device, further cause the electronic device to: select adirection of adjustment, or a magnitude of adjustment, or both based atleast in part on the comparison, wherein the adjusting the readthreshold from the first value to the second value is in accordance withthe selected direction of adjustment, or the selected magnitude ofadjustment, or both.
 13. The non-transitory computer-readable medium ofclaim 10, wherein the instructions, when executed by the processor ofthe electronic device, further cause the electronic device to: determinethat the quantity of memory cells indicated as corresponding to thelogic value satisfies a threshold, wherein adjusting the read thresholdfrom the first value to the second value is based at least in part onthe determination that the quantity of memory cells indicated ascorresponding to the logic value satisfies the threshold.
 14. Thenon-transitory computer-readable medium of claim 13, wherein theinstructions, when executed by the processor of the electronic device,further cause the electronic device to: select a direction ofadjustment, or a magnitude of adjustment, or both based at least in parton the determination that the quantity of memory cells indicated ascorresponding to the logic value satisfies the threshold, whereinadjusting the read threshold from the first value to the second value isin accordance with the selected direction of adjustment, or the selectedmagnitude of adjustment, or both.
 15. The non-transitorycomputer-readable medium of claim 10, wherein the instructions, whenexecuted by the processor of the electronic device, further cause theelectronic device to: detect an error, using an error correction codescheme, after reading the plurality of memory cells using the readthreshold having the first value; and determine that the error isuncorrectable for the error correction code scheme, wherein adjustingthe read threshold is based at least in part on the determination thatthe error is uncorrectable for the error correction code scheme.
 16. Thenon-transitory computer-readable medium of claim 10, wherein the readthreshold comprises a voltage threshold, a current threshold, or acombination thereof.
 17. The non-transitory computer-readable medium ofclaim 10, wherein the instructions, when executed by the processor ofthe electronic device, further cause the electronic device to: detect anerror based at least in part on reading the plurality of memory cellsusing the read threshold having the second value; and adjust the readthreshold from the second value to a third value based at least in parton the detected error.
 18. A method performed by a memory device, themethod comprising: reading a plurality of memory cells of a memory arrayof the memory device using a read threshold having a first value;adjusting the read threshold from the first value to a second valuebased at least in part on a quantity of memory cells of the plurality ofmemory cells indicated, by the reading using the read threshold havingthe first value, as corresponding to a logic value of a plurality oflogic values; and reading the plurality of memory cells of the memoryarray using the read threshold having the second value.
 19. The methodof claim 18, further comprising: comparing the quantity of memory cellsindicated as corresponding to the logic value to a second quantity ofmemory cells of the plurality of memory cells indicated, by the readingusing the read threshold having the first value, as corresponding to asecond logic value of the plurality of logic values, wherein adjustingthe read threshold from the first value to the second value is based atleast in part on the comparison.
 20. The method of claim 19, furthercomprising: selecting a direction of adjustment, or a magnitude ofadjustment, or both based at least in part on the comparison.